Cesarean Section, Fetal Monitoring, and Perinatal Mortality in California RONALD L. WILLIAMS, PHD, AND WARREN E. HA VES, MD
Abstract: The rate of cesarean section in California has been growing at a compound rate of about 10 per cent per annum since 1969, coinciding with the advent of fetal monitoring. It is of interest, therefore, to study the distribution and efficacy of obstetric interventions. Information derived from the 1977 California birth cohort and a survey questionnaire was used to study the factors associated with the rate of cesarean section in 323 hospitals. Significant positive correlations were observed between the cesarean rate (CSR) and hospital factors indicative of a high degree of technology, including the proportion of labors electronically monitored. Significant negative correlations were
observed between the CSR and hospital-specific variables suggestive of socioeconomically underprivileged patient populations. Other factors being constant, hospitals characterized by prepayment health care financing also had lower CSRs. A standaridized mortality ratio (SMR) based on 2.3 million births in the 1970-1976 cohorts was used to adjust the 1977 hospital specific perinatal mortality rates for birth weight, gestational age, sex, race, and plurality. The results show that hospitals which intervene technologically in a large proportion of births have lower risk adjusted perinatal mortality rates. (Am J Public Health 69:864-870,
Introduction
Magnifying this interest has been consumer concern regarding monetary and emotional costs of operative deliveries
The cesarean section rate (CSR) in California, as elsewhere, began increasing rapidly in the late 1960s.1-3 Reasons for the increase are not totally understood; however, several other important perinatal events occurred during the same period: 1) the advent of electronic fetal monitoring; 2) the increased access of premature infants to neonatal intensive care; 3) the change in indications for the use of cesarean sections, particularly in the delivery of primipara breeches, and in the management of abnormal descent patterns with borderline cephalo-pelvic disproportion.4-9 Early clinical evidence suggested that these events had a positive impact on perinatal and neonatal survival.I0-II The association between cesarean section rates and perinatal outcomes is also demonstrated by California's vital statistics. In 1965, the CSR was 5.1 per cent and by 1977 it had risen to 15.4 per cent of all deliveries, an increase of 202 per cent (Table 1). In 1966, the perinatal mortality rate was 27.1 per 1000 births, but by 1977 it had dropped by 30 per cent to 16.5 per 1000. However, the association of cesarean section with post-operative complications, including an increased incidence of respiratory distress syndrome, has recently brought the rapidly growing CSR under closer scrutiny.5' 12-17
and their effect on mother-infant bonding. Finally, the magnitude of the phenomenon is disconcerting; beginning in 1969 the CSR grew at a compound rate of 9-12 per cent per annum yielding a doubling time of about six years. This paper explores the association between hospitalspecific cesarean section rates, fetal monitoring rates, and standardized perinatal mortality ratios in California during 1977. In contrast with previous studies,4-" which were based on statistics from individual hospitals and often combining years of data, this study attempts to examine the prevailing patterns of obstetric practice over a broad geographical region.
Address reprint requests to Ronald L. Williams, PhD, Community and Organization Research Institute, University of California at Santa Barbara, Santa Barbara, CA 93106. Dr. Hawes is with the California State Department of Health Services. This paper, submitted to the Joumal September 29, 1978, was revised and accepted for publication May 17, 1979. Editor's Note: See also editorials pages 851, 852. 864
1979.)
Materials and Methods Information obtained from linked birth and death records for the 1977 California birth cohort was the major source of study data. The vital record information was used to compute the CSR for each hospital in the State and to form variables describing age, parity, ethnicity, and degree of prenatal care of mothers delivering in each hospital, as well as legitimacy, plurality, birth weight, and perinatal outcome of infants. Data related to the percentage of monitored deliveries, the percentage of births attended by physician type, and the presence of a perinatal mortality study committee were obtained by means of a hospital survey questionnaire administered by the California Department of Health Services in March 1977. The 323 responses to the 350 mailed questionnaires accounted for 324,085 births, or 94 per cent of the AJPH September 1979, Vol. 69, No. 9
CESAREAN SECTION AND PERINATAL MORTALITY TABLE 1 -Cesarean Section and Perinatal Mortality in California, 1966-77 Cesarean Section Year
1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977
Total Births
Cesarean Sections
343,092 342,077 344,716 358,208 357,991
17,978 18,438 19,373 22,316 25,298 25,529 27,028 29,883 35,661 40,995 47,089 54,006
334,379 310,628 301,943 316,020 321,464 336,384 351,575
Rate
(CSR)
5.2 5.4 5.6 6.2 6.9 7.6 8.7 9.9 11.3 12.8 14.0 15.4
total identifiable hospital births in 1977; these 323 hospitals constitute the sample for this study. Additional hospital-specific information was obtained from other sources. Included were such attributes as type of ownership, teaching affiliation, and the presence of a certified neonatal intensive care unit (NICU). The variables defined in Table 2 were chosen because they were indicative of different approaches to modem obstetrical practice, or had been previously described as having strong associations with cesarean section rates or with perinatal outcomes, or were related to the distribution and financing of medical care. While most variables are rate or percentage measures, a number of qualitative or categorical variables are defined in a binary fashion. For example, for hospital ownership, "Federal" assumes one of two values: "0" if the ownership/control is nonfederal, or " I" if the hospital is federally owned. The Standardized Mortality Ratio (SMR), an indirect method of adjusting for risk, is computed by comparing the observed number of perinatal deaths with the expected number.18-19 The number of expected deaths is based primarily on birth weight, the crucial intervening variable in a causal sequence leading from the condition of the fetus to perinatal outcome. The independent effects of four other risk-related newborn attributes (gestational age, sex, race, and plurality) are accounted for as well. Birth weight was divided into 18 categories of 250 g intervals, gestational age into 14 categories of two-week intervals, and race into four classes with separate reference rates computed for males, females, single, and multiple births. To obtain a reasonable degree of precision using such a potentially large number of cells, the total 1970-1976 California cohort (2.3 million births) was used as the standard population. After cells with few or no events were eliminated, a total of 1,172 attribute-specific standard population perinatal mortality rates were available. The adjustment is "indirect" since the expected number of deaths is computed on the assumption that the attribute-specific rates for each hospital are equal to those for the standard population. Once the expected number of perinatal deaths was computed, the SMR was obtained by dividing the number of obAJPH September 1979, Vol. 69, No. 9
Perinatal
Annual Per Cent Increase in CSR
Per Cent Increase in CSR Since 1965
Rate (per 1 000)
2 3 4 10 9 10 12 12 12 12 9 10
2 5 10 21 34 49 69 93 120 149 173 202
27.1 26.0 25.7 24.9 23.6 22.3 21.4 20.2 19.5 18.6 17.9 16.5
Mortality
served perinatal deaths in a given hospital by the number expected, and multiplying by 100 to convert into percentage units. An SMR less than 100 indicates above-average care, while one greater than 100 suggests below average effectiveness in preventing intra-and post-partum deaths. Because of the crucial role played by birth weight in the SMR TABLE 2-Variables under Study for each Hospital
Hospital Ownership District hospital (1-yes, 0-no) District Federal government hospital (1-yes, 0-no) Federal Kaiser Foundation hospital (1-yes, 0-no) Kaiser Local government hospital (1-yes, 0-no) Local Private non-profit hospital (1-yes, 0-no) Nonprofit Private for-profit hospital (1-yes, 0-no) Profit University of California hospital (1-yes, 0-no) University Technological Indicators General Percentage deliveries by generalists or general surgeons Percentage deliveries monitored electronically Monitor NICU Neonatal intensive care unit (1-yes, 0-no) Percentage deliveries by board-certified Ob/Gyn obstetricians Perinatal mortality study committee (1-yes, Peristudy
0-no) ACOG-approved residency in obstetrics (1-yes, 0-no) Matemal and Newborn Variables Percentage normal age mothers (18 to 35) Normalage Older Percentage older mothers (35 or older) Percentage adolescent mothers (less than 18) Teenage Percentage primiparas Paral Para5 Percentage mothers parity 5 or greater Percentage older primiparas Oldparal Lt2501 G Percentage births weighing less than 2501 Teaching
grams Percentage multiple births Multiple Ethnic and Socioeconomic Indicators Percentage black deliveries Black Percentage Spanish surname births Spanish White Percentage white non-Spanish births Percentage out-of-wedlock births Illegitimate Percentage mothers having no prenatal care Noprenatal Outcome-related Variables CSR Percentage deliveries by cesarean section SMR Standardized mortality ratio
865
WILLIAMS AND HAWES
methodology, births with unknown weights were omitted; these, however, represent only 0.2 per cent of the total. Also omitted were infants weighing less than 500 g, since such infants very rarely survive and are likely to have experienced less than 20 weeks of gestation. This procedure was used to ensure that the computed mortality rate conformed to the "Perinatal II" definition of death as occurring from the twentieth week of pregnancy through the twenty-seventh day of life. Relationships between the variables were studies using correlation and multiple regression methods. A forward stepwise multiple regression procedure20 was applied to isolate the most significant independent correlations of the study variables with CSR and with SMR. Because the original observations (individual births) have been grouped by hospital, the usual assumptions for ordinary least squares estimation do not directly apply. When data are grouped, the sampling error of the SMR variable will be approximately inversely proportional to the square root of the number of expected deaths in each hospital, and it is necessary to apply weighted least squares in order to achieve efficiency in the estimation process. Because the size of delivery service varied widely, the product-moment correlation coefficients were also weighted. Details concerning the weighted and stepwise regression procedures have been summarized elsewhere. 19-21 The distribution of births in the study sample by type of hospital ownership and ethnicity of child is reported in Table 3. The local government category includes county and city hospitals. In California, these hospitals tend to serve a high proportion of medically indigent mothers, many of whom have Spanish surnames. Although three of the five stateowned University of California hospitals were countyowned at the beginning of the study period, their emphasis on teaching and research warrants their consideration as a
separate group. District hospitals are frequently found in rural areas where a hospital district is formed to satisfy unmet needs for medical care and thus serve a more heterogeneous
population. Federally-owned hospitals having maternity services comprise military facilities serving armed forces personnel and their dependents on a no-cost basis. The not-for-profit Kaiser Hospitals belong to the Kaiser-Permanente Medical Care program, a large prepaid group practice plan. The income of the individual physicians of the Permanente Medical Groups is larely unrelated to the services provided, but there are some financial incentives for the group to limit services to those that are medically indicated. The physicians of private nonprofit and proprietary hospitals are reimbursed on a fee-for-service basis. Some critics of prepaid group practice plans believe that they may not provide enough surgery. But others argue that fee-forservice incentives result in excess surgery.22
Results The mean number of deliveries for the 323 hospitals was
1,003 with 88.6 per cent of all deliveries occurring in urban hospitals. Teaching hospitals accounted for 22.9 per cent of the sample births with 16.4 per cent occurring in hospitals having a certified neonatal intensive care unit. The CSR ranged from zero to 28.9 per cent with an average of 15.4 per cent. From the survey results it was estimated that more than one-half (54 per cent) of all deliveries in California were electronically monitored in 1977. Higher cesarean section rates were significantly correlated with hospitals having a high proportion of obstetricianattended deliveries, nonprofit ownership, a high proportion of electronically monitored deliveries, and a perinatal study committee (Table 4). Hospitals having higher proportions of
TABLE 3-Distribution of Births by Type of Hospital Ownership and Birth Ethnicltya Number of Births Hospital
Number of
White
White
Ownership
Hospitals
Non-Spanish
Spanish
District Federal
Kaiser Local
Nonprofit Profit
University TOTAL
48 14 13
33 144
66 5
323
Other
Black
Ethnicities
All Races
Per Cent of Total Births
16,534
6,206
791
1,453
24,984
(66.2)
(24.8)
704
(3.2)
1,190
(5.8)
1,279
(100.0)
(66.8)
20,773
(7.4)
7,984
(12.4)
(13.4)
(100.0)
(56.1)
11,986
(21.6)
25,887
(12.7)
4,564
(9.6)
1,721
(100.0)
(58.6)
88,553
(10.3)
37,088
(3.9)
-44,158
13.6
(27.2)
15,792
46.9
(58.2)
22,415
(24.4)
15,760
(10.4)
5,633
10,594 (7.0) 1,744
(100.0) 152,027
(49.2)
(34.6)
(12.4)
(3.8)
(40.5) 171,014 (52.8)
(43.3)
(8-3)
(7.9)
6,394
4,359
4,668
4,694
894
3,574
851
98,297
33,558
21,216
(30.3)
(10.4)
(6.5)
9,567
37,025
(100.0)
45,552 (100.0) 10,772 (100.0) 324,085 (100.0)
7.7 3.0 11.4
14.1 3.3
100.0
aNumbers in parenthesis are percentages of row totals. Example: 58.6 per cent of the 44,158 births occurring in hospitals owned by local govemments were classified as white Spanish-sumame.
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CESAREAN SECTION AND PERINATAL MORTALITY Table 4-Study Variables Having Statistically Significant Correlations with Cesarean Section Rate (CSR) Positively Correlated
Negatively Correlated
Study Variable
Correlation Coefficient
Level of Significance
Variable
Ob/Gyn White Paral Nonprofit Monitor Normalage
0.333 0.330 0.327 0.287 0.259 0.251 0.248 0.117
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0353
Spanish Noprenatal Teenage Local Illegitimate General
Oldparal Peristudy
primiparas and older primiparas also tend to have higher CSRs, and cesarean deliveries tend to be performed more often in hospitals serving larger proportions of white nonSpanish mothers and mothers between the ages of 18 and 35 years. Variables having significant negative associations with CSR are mostly maternal variables with a conspicuous absence of technological indicators. Hospitals in this group tend to serve adolescent or Spanish surname mothers, or those having no prenatal care, delivering out-of-wedlock, or of high parity. Furthermore, these hospitals tend to have larger proportions of deliveries by generalists or are Kaiserowned or owned by local governments. Table 5 shows the six variables that entered the CSR stepwise regression equation at the pre-set p < .05 level of significance, accounting for almost 40 per cent of the variance in the cesarean section rates between the 323 hospitals (R-square = 0.3725). The first three variables-per cent high parity mothers, per cent labors electronically monitored, and per cent deliveries by obstetricians-together account for about 30 per cent of the variance. This intermediate result indicates that fetal monitoring is positively correlated with an increased cesarean section rate, even after accounting for an inverse measure of maternal need (percentage parity five or greater) as well as the higher number of obstetrician-assisted deliveries usually associated with monitoring. The Kaiser ownership variable, entering with a negative coefficient in the fourth step, suggests that prepayment has an independent attenuating impact on the rate of surgical inTable 5-Study Variables Entering in Final CSR Stepwise Regression Equation Step
Regression
Entered
Variable
Coefficient
0 1 2 3
Intercept Para5 Monitor
-0.988
4 5 6
Kaiser Older White
Ob/Gyn
Signific4nce Level of Coefficient
9.609
0.037 0.024
-2.965
0.0001 0.0001 0.0001
0.0001
0.558 0.027
0.0001 0.0238
AJPH September 1979, Vol. 69, No. 9
Study Para5
Kaiser
Correlation Coefficient
Level of Significance
-0.371 -0.333 -0.296 -0.283 -0.228 -0.212 -0.198 -0.137
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0003 0.0136
tervention. Holding other factors constant, Kaiser hospitals as a group have a CSR that is about three percentage points
lower than all non-Kaiser hospitals. These results raise questions regarding the relationship between SMR, CSR, and other hospital factors. Since the purpose of the remaining anaylsis is to study the variation of adjusted perinatal mortality rates according to hospital characteristics, the maternal age-parity and newborn factors described in Table 2 are not used in this context. The strongest correlation observed is a negative one between SMR and CSR (Table 6). There is also a significant negative correlation between SMR and the percentage monitored. Other variables negatively correlated with SMR include presence of a neonatal intensive care unit, private nonprofit ownership, and per cent white non-Spanish births. Variables positively correlated with SMR include local government ownership, per cent deliveries by generalists, per cent Spanish surname mothers, and per cent mothers having no prenatal care. These correlations are consistent with the CSR-
Table 6-Correlation Coefficients between Study Variables and Standardized Mortality Ratio (SMR) Study Variable
Correlation Coefficient
Level of Significance
Black CSR District Federal General Illegitimate Kaiser Local Monitor NICU Noprenatal Nonprofit Ob/Gyn Peristudy Profit Spanish Teaching University White
-0.001 -0.329 -0.007 -0.049 0.143 0.099 0.058 0.196 -0.172 -0.136 0.126 -0.146 -0.096 -0.025 0.059 0.302 -0.102 -0.129 -0.250
0.9823 0.0001 0.9020 0.3802 0.0104 0.0741 0.2998 0.0004 0.0019 0.0141 0.0239 0.0084 0.0839 0.6536 0.2917 0.0001 0.0656 0.0206 0.0001
867
WILLIAMS AND HAWES TABLE 7-Mean Values of Selected Variables for Study Hospitals by Grouped Cesarean Section Rate' Cesarean Section Rate (CSR)
Variable
General Ob/Gyn Monitor SMR Number of Hospitals
0.0-4.9
5.0-9.9
10.0-14.9
15.0-19.9
20.0-24.9
25+
Total
(%)
(%)
(%)
(%)
(%)
(%)
(%)
59 26 14 108 15
60 25 28 105 37
18 56 46 87 115
17 72 53 84 108
9 79 65 75 44
2 98 65 70 4
23 60 48 88 323
aExample: 15 of the 323 hospitals had CSR < 5% with an average of 59% of deliveries attended by generalists.
related results showing that hospitals which perform fewer cesarean sections tend to have higher SMRs. Table 7 reports the SMR and three technological indicators (General, Ob/Gyn, and Monitor) for hospitals classified according to CSR in five percentage point intervals. It is clear that hospitals with proportionately more technological interventions have lower standardized mortality ratios. The weighted stepwise regression results for SMR are reported in Table 8. Three variables explained 25 per cent of the variance in the standardized indexes. Significant independent negative associations are observed between SMR and cesarean section rate as well as the presence of a neonatal intensive care unit. Additionally, a significant independent positive association exists between SMR and per cent white Spanish births. These results suggest that hospitals disposed toward technology have lower SMRs and, after the degree of technological intervention is accounted for, hospitals having larger proportions of Spanish-surname mothers have higher standardized mortality rates. TABLE 8-SMR Stepwise Regression Models With CSR Included Step Entered
Variable
Regression Coefficient
0 1 2 3
Intercept CSR Spanish NICU
95.322 - 1.281 0.261
-10.939
Significance Level of
Coefficient
0.0001 0.0001 0.0001
With CSR Suppressed
Step Entered
0 1 2 3 4 5
868
Variable
Regression Coefficient
Intercept Spanish
68.734 0.364
NICUJ Kaiser Black General
-10.806 8.241 0.133 0.110
When suppressing the CSR variable, the stepwise procedure shows that "Spanish" and NICU" are once again strongly associated with SMR. In this context, it is important to note that statewide differentials in fetal viability by ethnic group for given birth weights and gestations have already been accounted for in SMR. The entry of the "Spanish" variable into the regression models indicates that hospitals having proportionately more Spanish-surname deliveries tend to provide less effective intra-and post-partum care. The regression results also indicate that, after accounting for a variety of factors, perinatal mortality rates are about 11 per cent lower in hospitals having an NICU than those that do not. With CSR suppressed, several 4dditional variables associated with lower CSRs enter the SMR equation with positive coefficients. It was shown earlier that the cesarean section rate is lower in hospitals having high percentages of deliveries by generalists and in Kaiser owned hospitals. Such hospitals tend to be independently tissociated with higher adjusted perinatal mortality rates when CSR is suppressed from the regression model. Further, while a high CSR is independently correlated with a high proportion of white non-Spanish deliveries (Table 5), a high SMR is associated with the complementary variables, "Black" and "Spanish" (Table 8). Again, hospitals having higher cesarean section rates have lower standardized perinatal mortality ratios.
Signfficance Level of Coefficient 0.0001 0.0002 0.0367 0.0776 0.1011
Discussion The advent of electronic fetal monitoring and the increased rate of cesarean section are said to reduce birth trauma and perinatal mortality.4-5 " If all births are to benefit from such practices, it is important to determine the distribution of their use. Also, in view of the rapid increase in cesarean section rates, some conclusion must be drawn as to the optimum level. This analysis revealed significant correlations between cesarean section rates and a number of maternal and hospital factors. Based on current modes of obstetric practice, many of the observed associations were as anticipated, yet others raised questions concerning the equity of access to modern obstetrical procedures. While the increase in CSR in primiAJPH September 1979,
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CESAREAN SECTION AND PERINATAL MORTALITY
parous mothers and in older primiparas might be expected on the basis of maternal risk considerations, the lower rates for hospitals serving greater proportions of Spanish-surname mothers, mothers having no prenatal care, out-of-wedlock and adolescent mothers is perplexing. Perhaps the medical need for a cesarean delivery is lower for such mothers, yet it is also possible that hospitals associated with high proportions of these patient types may have lagged in utilizing modern obstetric technology. By most measures of maternal and newborn risk, such patients are likely to require more sophisticated obstetric services, but in fact receive proportionately fewer cesareans. This result suggests a potential misallocation of medical resources. Similarly, it was surprising to find the two newborn variables, low birth weight and multiple births, not significantly correlated with CSR. In the case of multiple births, this result may be due to little variation between hospitals for that variable since the occurrence of multiple births is likely to be uniformly distributed. Most of the hospital variables indicative of the level of sophistication of obstetrical practice are significantly correlated with the cesarean rate, and some of these variables continue to display independent associations in the multiple regression results. These findings suggest that increasing cesarean rates are the medical profession's response to yet another "technological imperative"23 which was stimulated by the advent of fetal monitoring. The hospital ownership variables are central to understanding the impact of organized medical care services on the utilization of technological advances. The significant negative coefficient for Kaiser ownership in the CSR regression equation confirms the notion prepaid health care financing tends to have an independent attenuating effect on the rate of surgical interventions. Whether the lower rates are optimal or uiot is yet another question. Also, it is possible that the maternal risk characteristics may be different for patients served by Kaiser hospitals and that the regression equation in Table 5 does not adequately adjust for such characteristics. Overall, the results suggest those variables associated with a high cesarean section rate in hospitals, perhaps even cesarean section itself, may have a beneficial effect on perinatal outcomes. That is, hospitals with higher cesarean section rates, higher rates of fetal monitoring, higher proportions of obstetrician-attended deliveries, and the availability of neonatal intensive care have better perinatal outcomes. In summary, hospitals with a high degree of technological intervention have lower standardized perinatal mortality rates. There are, however, some important caveats. First, the SMR as presently defined accounts only for the condition of the newborn at the time of birth, and is not capable of adjusting for the possibility of iatrogenic prematurity. While each newborn's birth weight and gestational age are accounted for, it may be possible that a very high percentage of elective cesareans could tend to lower weight and gestation by causing a significant number of premature deliveries. However, as shown in Table 9, this does not seem to have occurred on a statewide basis since the expected perinatal mortality rate has been slowly declining. On the other hand, the observed AJPH September 1979, Vol. 69, No. 9
TABLE 9-Trends in Observed, Expected, and Standardized Perinatal Mortality Rates: California 1970-1977 Observed Perinatal Mortality Ratea
Expected Perinatal Mortality Rateb
Standardized Perinatal Mortality Ratioc
1970
21.3
1971 1972 1973 1974 1975 1976
20.1
18.9 18.1 18.2 18.2 17.8 17.8 17.7 17.4
112.9 110.5 105.7 98.8 95.3 89.1 86.9 81.3
Year
1977
19.2 17.9 17.0 15.8 15.4 14.2
aExcludes births of less than 500 g and those with unknown birth weights. bBased on statewide perinatal mortality rates for combined 1970-1976 birth cohorts.
CSMR =
100 x (observed rate . expected
rate).
rate has declined much more rapidly, thus yielding a 30 per cent decrease in SMR from 1970 through 1977. Second, the positive association between cesarean section rates and improved perinatal outcomes does not demonstrate a causal link between cesarean section and perinatal outcome for a given pregnancy. Hospitals performing proportionately more cesarean deliveries also have more specialized staffs and equipment, and a high cesarean section rate may be just an indicator for careful, sophisticated ob-
stetrical practice. Further, this study, while based on a large aggregate of births, focused on a single year and did not measure the impact of technological change over time. Third, the outcome measure used here does not address the issue of maternal morbidity and mortality. Even if a causal link between electronic monitoring, cesarean deliveries, and improved perinatal outcomes could be demonstrated, the question of increased maternal risks still remains.'3' '5 While the purpose of this analysis was to measure the effects of these technologies on mortality, there are other important considerations in the childbearing process that may be adversely affected by such interventions. Fourth, it is possible that improved perinatal outcomes could be achieved by other means. For example, programs for better prenatal nutrition to improve birth weight, and for ameliorating the ill effects of adolescent and out-of-wedlock pregnancies might achieve comparable savings in terms of actual perinatal loss. Finally, the increased costs of this technical approach to childbirth have not been discussed. These costs include not only the more intensive use of medical resources and increased lengths of stay, but also decreased maternal function following hospital discharge. Other indirect costs include the rising number of repeat cesarean sections resulting from the increased primary rate. With these caveats in mind, we cannot conclude that the current emphasis on technology in obstetrics is justified. However, the statistical results suggest that hospitals which use a greater proportion of technological interventions and have available sophisticated manpower and equipment do have better perinatal outcomes. 869
WILLIAMS AND HAWES
REFERENCES 1. Petitti D, Olson RO, Williams RL: Cesarean section in California: 1960-1975. Am J Obstet Gynecol 133:391-397, 1979 2. Lowe JA, Klassen DF, Loup RJ: Cesarean sections in U.S. PAS hospitals. PAS Reporter 14:1, 1976. 3. Johnell HE, Ostberg, H, Wahlstrand T: Increasing cesarean section rate. Acta Obstet Gynecol Scand 55:95-100, 1976. 4. Amato JC: Fetal monitoring in a community hospital. Obstet Gynecol 50:269-274, 1977. 5. Evrard JR, Gold EM: Cesarean section: risk/benefit. Perinatal Care 2:4-10, 1978. 6. Haverkamp HD, Thompson, HE, McFee JG, et al: The evaulation of continuous fetal heart monitoring in high risk pregnancy. Am J Obstet Gynecol 125:310-320, 1976. 7. Hibbard LT: Changing trends in cesarean section. Am J Obstet Gynecol i24:798-804, 1976. 8. Hughey MJ, LaPata RE, McElin TW, et al: The effect of fetal monitoring on the incidence of cesarean section. Obstet Gynecol 49:513-518, 1977. 9. Tutera G, Newman RL: Fetal monitoring: its effect on perinatal mortality and cesarean section rates and its complications. Am J Obstet Gynecol 122:750-754, 1975. 10. Neutra RR, Fienberg SE, Greenland S, et al: Effect of fetal monitoring on neonatal death rates. N Engl J Med 299:324-326, 1978. 11. Paul RH, Hon EH: Clinical fetal monitoring: effect on perinatal outcome. Am J Obstet Gynecol 118:529-533, 1974. 12. Baker RA: Technological Intervention in Obstetrics: has the pendulum swung too far? Obstet Gynecol 51:241-244, 1978. 13. Green SL, Sarubbi FA: Risk factors associated with post cesarean section febrile morbidity. Obstet Gynecol 49:686-690, 1977. 14. Hack M, Fanaroff AA, Klaus MH, et al: Neonatal respiratory distress following elective delivery: a preventable disease? Am J Obstet Gynecol 126:43-47, 1976.
15. Hagen D: Maternal febrile morbidity associated with fetal monitoring and cesarean section. Obstet Gynecol 46:260-262, 1975. 16. Maisels MJ, Rees R, Marks K, et al: Elective delivery of the term fetus: an obstetrical hazard. JAMA 238:2036-2039, 1977. 17. Reed DM, Bakketeig LS, Nugent RP: The epidemiology of respiratory distress syndrome in Norway. Am J Epidemiol 107:299-310, 1978. 18. Armitage P: Statistical Methods in Medical Research. Oxford: Blackwell, 1971. 19. Williams RL: Measuring the effectiveness of perinatal medical care. Medical Care 17:95-110, 1979. 20. Barr AJ, Goodnight JH, Sall JP, et al: A User's Guide to SAS 76. Raleigh: SAS Institute, 1976. 21. Buse A: Goodness of fit in generalized least squares estimation. Am Stat 27:106-108, 1973. 22. LaDou J, Likens JD: Medicine and Money. Cambridge: Ballinger, 1977. 23. Fuchs VR: Who Shall Live? New York: Basic Books, 1974.
ACKNOWLEDGMENTS Supported in part in Maternal and Child Health Grant No. MCR-060390-03 from the Bureau of Community Health Services, DHEW. This study was performed in cooperation with the staff of the Maternal and Child Branch of the California Department of Health Services. The authors are indebted to Diana Petitti and Mich Tashiro for a number of valuable contributions. Helpful comments on earlier drafts were received from Joseph Brazie, Siegried Centerwall, George Cunningham, Lyn Headley, Russell Laros, Frank Norris, and Roderic Phibbs. William Mason assisted in processing the sample data.
APHA 107th Annual Meeting
Epildemiologic Exchange
Deadline for Abstracts is October 1 The Epidemiology Section of the American Public Health Association will again sponsor the annual Epidemiologic Exchange on Wednesday, November 7, 1979, from 2pm to 5pm, during the APHA Annual Meeting in New York City. The session will be held at the Sheraton Centre, Princess Room. Abstracts are now being invited by Dr. Michael B. Gregg, organizer and presider of the session. The deadline for submission of abstracts is October 1. Abstracts should be limited to 200 words; no special abstract form is required. This annual forum presents the latest findings in epidemiologic investigations from around the world. Approximately 12 presentations can be accepted for this symposium. The oral presentations are limited to about 15 minutes each. Papers to be presented at this session will summarize "late-breaking" epidemiologic investigations, studies, and methodologies which have been conceived, conducted, and/or concluded during the last 6-12 months. Send abstracts to: Dr. Michael B. Gregg, Deputy Director, Bureau of Epidemiology, Center for Disease Control DHEW/PHS, Atlanta, GA 30333. Telephone 404/329-3636.
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AJPH September 1979, Vol. 69, No. 9
Abstract: The rate of cesarean section in California has been growing at a compound rate of about 10 per cent per annum since 1969, coinciding with the advent of fetal monitoring. It is of interest, therefore, to study the distribution and efficacy of obstetric interventions. Information derived from the 1977 California birth cohort and a survey questionnaire was used to study the factors associated with the rate of cesarean section in 323 hospitals. Significant positive correlations were observed between the cesarean rate (CSR) and hospital factors indicative of a high degree of technology, including the proportion of labors electronically monitored. Significant negative correlations were
observed between the CSR and hospital-specific variables suggestive of socioeconomically underprivileged patient populations. Other factors being constant, hospitals characterized by prepayment health care financing also had lower CSRs. A standaridized mortality ratio (SMR) based on 2.3 million births in the 1970-1976 cohorts was used to adjust the 1977 hospital specific perinatal mortality rates for birth weight, gestational age, sex, race, and plurality. The results show that hospitals which intervene technologically in a large proportion of births have lower risk adjusted perinatal mortality rates. (Am J Public Health 69:864-870,
Introduction
Magnifying this interest has been consumer concern regarding monetary and emotional costs of operative deliveries
The cesarean section rate (CSR) in California, as elsewhere, began increasing rapidly in the late 1960s.1-3 Reasons for the increase are not totally understood; however, several other important perinatal events occurred during the same period: 1) the advent of electronic fetal monitoring; 2) the increased access of premature infants to neonatal intensive care; 3) the change in indications for the use of cesarean sections, particularly in the delivery of primipara breeches, and in the management of abnormal descent patterns with borderline cephalo-pelvic disproportion.4-9 Early clinical evidence suggested that these events had a positive impact on perinatal and neonatal survival.I0-II The association between cesarean section rates and perinatal outcomes is also demonstrated by California's vital statistics. In 1965, the CSR was 5.1 per cent and by 1977 it had risen to 15.4 per cent of all deliveries, an increase of 202 per cent (Table 1). In 1966, the perinatal mortality rate was 27.1 per 1000 births, but by 1977 it had dropped by 30 per cent to 16.5 per 1000. However, the association of cesarean section with post-operative complications, including an increased incidence of respiratory distress syndrome, has recently brought the rapidly growing CSR under closer scrutiny.5' 12-17
and their effect on mother-infant bonding. Finally, the magnitude of the phenomenon is disconcerting; beginning in 1969 the CSR grew at a compound rate of 9-12 per cent per annum yielding a doubling time of about six years. This paper explores the association between hospitalspecific cesarean section rates, fetal monitoring rates, and standardized perinatal mortality ratios in California during 1977. In contrast with previous studies,4-" which were based on statistics from individual hospitals and often combining years of data, this study attempts to examine the prevailing patterns of obstetric practice over a broad geographical region.
Address reprint requests to Ronald L. Williams, PhD, Community and Organization Research Institute, University of California at Santa Barbara, Santa Barbara, CA 93106. Dr. Hawes is with the California State Department of Health Services. This paper, submitted to the Joumal September 29, 1978, was revised and accepted for publication May 17, 1979. Editor's Note: See also editorials pages 851, 852. 864
1979.)
Materials and Methods Information obtained from linked birth and death records for the 1977 California birth cohort was the major source of study data. The vital record information was used to compute the CSR for each hospital in the State and to form variables describing age, parity, ethnicity, and degree of prenatal care of mothers delivering in each hospital, as well as legitimacy, plurality, birth weight, and perinatal outcome of infants. Data related to the percentage of monitored deliveries, the percentage of births attended by physician type, and the presence of a perinatal mortality study committee were obtained by means of a hospital survey questionnaire administered by the California Department of Health Services in March 1977. The 323 responses to the 350 mailed questionnaires accounted for 324,085 births, or 94 per cent of the AJPH September 1979, Vol. 69, No. 9
CESAREAN SECTION AND PERINATAL MORTALITY TABLE 1 -Cesarean Section and Perinatal Mortality in California, 1966-77 Cesarean Section Year
1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977
Total Births
Cesarean Sections
343,092 342,077 344,716 358,208 357,991
17,978 18,438 19,373 22,316 25,298 25,529 27,028 29,883 35,661 40,995 47,089 54,006
334,379 310,628 301,943 316,020 321,464 336,384 351,575
Rate
(CSR)
5.2 5.4 5.6 6.2 6.9 7.6 8.7 9.9 11.3 12.8 14.0 15.4
total identifiable hospital births in 1977; these 323 hospitals constitute the sample for this study. Additional hospital-specific information was obtained from other sources. Included were such attributes as type of ownership, teaching affiliation, and the presence of a certified neonatal intensive care unit (NICU). The variables defined in Table 2 were chosen because they were indicative of different approaches to modem obstetrical practice, or had been previously described as having strong associations with cesarean section rates or with perinatal outcomes, or were related to the distribution and financing of medical care. While most variables are rate or percentage measures, a number of qualitative or categorical variables are defined in a binary fashion. For example, for hospital ownership, "Federal" assumes one of two values: "0" if the ownership/control is nonfederal, or " I" if the hospital is federally owned. The Standardized Mortality Ratio (SMR), an indirect method of adjusting for risk, is computed by comparing the observed number of perinatal deaths with the expected number.18-19 The number of expected deaths is based primarily on birth weight, the crucial intervening variable in a causal sequence leading from the condition of the fetus to perinatal outcome. The independent effects of four other risk-related newborn attributes (gestational age, sex, race, and plurality) are accounted for as well. Birth weight was divided into 18 categories of 250 g intervals, gestational age into 14 categories of two-week intervals, and race into four classes with separate reference rates computed for males, females, single, and multiple births. To obtain a reasonable degree of precision using such a potentially large number of cells, the total 1970-1976 California cohort (2.3 million births) was used as the standard population. After cells with few or no events were eliminated, a total of 1,172 attribute-specific standard population perinatal mortality rates were available. The adjustment is "indirect" since the expected number of deaths is computed on the assumption that the attribute-specific rates for each hospital are equal to those for the standard population. Once the expected number of perinatal deaths was computed, the SMR was obtained by dividing the number of obAJPH September 1979, Vol. 69, No. 9
Perinatal
Annual Per Cent Increase in CSR
Per Cent Increase in CSR Since 1965
Rate (per 1 000)
2 3 4 10 9 10 12 12 12 12 9 10
2 5 10 21 34 49 69 93 120 149 173 202
27.1 26.0 25.7 24.9 23.6 22.3 21.4 20.2 19.5 18.6 17.9 16.5
Mortality
served perinatal deaths in a given hospital by the number expected, and multiplying by 100 to convert into percentage units. An SMR less than 100 indicates above-average care, while one greater than 100 suggests below average effectiveness in preventing intra-and post-partum deaths. Because of the crucial role played by birth weight in the SMR TABLE 2-Variables under Study for each Hospital
Hospital Ownership District hospital (1-yes, 0-no) District Federal government hospital (1-yes, 0-no) Federal Kaiser Foundation hospital (1-yes, 0-no) Kaiser Local government hospital (1-yes, 0-no) Local Private non-profit hospital (1-yes, 0-no) Nonprofit Private for-profit hospital (1-yes, 0-no) Profit University of California hospital (1-yes, 0-no) University Technological Indicators General Percentage deliveries by generalists or general surgeons Percentage deliveries monitored electronically Monitor NICU Neonatal intensive care unit (1-yes, 0-no) Percentage deliveries by board-certified Ob/Gyn obstetricians Perinatal mortality study committee (1-yes, Peristudy
0-no) ACOG-approved residency in obstetrics (1-yes, 0-no) Matemal and Newborn Variables Percentage normal age mothers (18 to 35) Normalage Older Percentage older mothers (35 or older) Percentage adolescent mothers (less than 18) Teenage Percentage primiparas Paral Para5 Percentage mothers parity 5 or greater Percentage older primiparas Oldparal Lt2501 G Percentage births weighing less than 2501 Teaching
grams Percentage multiple births Multiple Ethnic and Socioeconomic Indicators Percentage black deliveries Black Percentage Spanish surname births Spanish White Percentage white non-Spanish births Percentage out-of-wedlock births Illegitimate Percentage mothers having no prenatal care Noprenatal Outcome-related Variables CSR Percentage deliveries by cesarean section SMR Standardized mortality ratio
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WILLIAMS AND HAWES
methodology, births with unknown weights were omitted; these, however, represent only 0.2 per cent of the total. Also omitted were infants weighing less than 500 g, since such infants very rarely survive and are likely to have experienced less than 20 weeks of gestation. This procedure was used to ensure that the computed mortality rate conformed to the "Perinatal II" definition of death as occurring from the twentieth week of pregnancy through the twenty-seventh day of life. Relationships between the variables were studies using correlation and multiple regression methods. A forward stepwise multiple regression procedure20 was applied to isolate the most significant independent correlations of the study variables with CSR and with SMR. Because the original observations (individual births) have been grouped by hospital, the usual assumptions for ordinary least squares estimation do not directly apply. When data are grouped, the sampling error of the SMR variable will be approximately inversely proportional to the square root of the number of expected deaths in each hospital, and it is necessary to apply weighted least squares in order to achieve efficiency in the estimation process. Because the size of delivery service varied widely, the product-moment correlation coefficients were also weighted. Details concerning the weighted and stepwise regression procedures have been summarized elsewhere. 19-21 The distribution of births in the study sample by type of hospital ownership and ethnicity of child is reported in Table 3. The local government category includes county and city hospitals. In California, these hospitals tend to serve a high proportion of medically indigent mothers, many of whom have Spanish surnames. Although three of the five stateowned University of California hospitals were countyowned at the beginning of the study period, their emphasis on teaching and research warrants their consideration as a
separate group. District hospitals are frequently found in rural areas where a hospital district is formed to satisfy unmet needs for medical care and thus serve a more heterogeneous
population. Federally-owned hospitals having maternity services comprise military facilities serving armed forces personnel and their dependents on a no-cost basis. The not-for-profit Kaiser Hospitals belong to the Kaiser-Permanente Medical Care program, a large prepaid group practice plan. The income of the individual physicians of the Permanente Medical Groups is larely unrelated to the services provided, but there are some financial incentives for the group to limit services to those that are medically indicated. The physicians of private nonprofit and proprietary hospitals are reimbursed on a fee-for-service basis. Some critics of prepaid group practice plans believe that they may not provide enough surgery. But others argue that fee-forservice incentives result in excess surgery.22
Results The mean number of deliveries for the 323 hospitals was
1,003 with 88.6 per cent of all deliveries occurring in urban hospitals. Teaching hospitals accounted for 22.9 per cent of the sample births with 16.4 per cent occurring in hospitals having a certified neonatal intensive care unit. The CSR ranged from zero to 28.9 per cent with an average of 15.4 per cent. From the survey results it was estimated that more than one-half (54 per cent) of all deliveries in California were electronically monitored in 1977. Higher cesarean section rates were significantly correlated with hospitals having a high proportion of obstetricianattended deliveries, nonprofit ownership, a high proportion of electronically monitored deliveries, and a perinatal study committee (Table 4). Hospitals having higher proportions of
TABLE 3-Distribution of Births by Type of Hospital Ownership and Birth Ethnicltya Number of Births Hospital
Number of
White
White
Ownership
Hospitals
Non-Spanish
Spanish
District Federal
Kaiser Local
Nonprofit Profit
University TOTAL
48 14 13
33 144
66 5
323
Other
Black
Ethnicities
All Races
Per Cent of Total Births
16,534
6,206
791
1,453
24,984
(66.2)
(24.8)
704
(3.2)
1,190
(5.8)
1,279
(100.0)
(66.8)
20,773
(7.4)
7,984
(12.4)
(13.4)
(100.0)
(56.1)
11,986
(21.6)
25,887
(12.7)
4,564
(9.6)
1,721
(100.0)
(58.6)
88,553
(10.3)
37,088
(3.9)
-44,158
13.6
(27.2)
15,792
46.9
(58.2)
22,415
(24.4)
15,760
(10.4)
5,633
10,594 (7.0) 1,744
(100.0) 152,027
(49.2)
(34.6)
(12.4)
(3.8)
(40.5) 171,014 (52.8)
(43.3)
(8-3)
(7.9)
6,394
4,359
4,668
4,694
894
3,574
851
98,297
33,558
21,216
(30.3)
(10.4)
(6.5)
9,567
37,025
(100.0)
45,552 (100.0) 10,772 (100.0) 324,085 (100.0)
7.7 3.0 11.4
14.1 3.3
100.0
aNumbers in parenthesis are percentages of row totals. Example: 58.6 per cent of the 44,158 births occurring in hospitals owned by local govemments were classified as white Spanish-sumame.
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CESAREAN SECTION AND PERINATAL MORTALITY Table 4-Study Variables Having Statistically Significant Correlations with Cesarean Section Rate (CSR) Positively Correlated
Negatively Correlated
Study Variable
Correlation Coefficient
Level of Significance
Variable
Ob/Gyn White Paral Nonprofit Monitor Normalage
0.333 0.330 0.327 0.287 0.259 0.251 0.248 0.117
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0353
Spanish Noprenatal Teenage Local Illegitimate General
Oldparal Peristudy
primiparas and older primiparas also tend to have higher CSRs, and cesarean deliveries tend to be performed more often in hospitals serving larger proportions of white nonSpanish mothers and mothers between the ages of 18 and 35 years. Variables having significant negative associations with CSR are mostly maternal variables with a conspicuous absence of technological indicators. Hospitals in this group tend to serve adolescent or Spanish surname mothers, or those having no prenatal care, delivering out-of-wedlock, or of high parity. Furthermore, these hospitals tend to have larger proportions of deliveries by generalists or are Kaiserowned or owned by local governments. Table 5 shows the six variables that entered the CSR stepwise regression equation at the pre-set p < .05 level of significance, accounting for almost 40 per cent of the variance in the cesarean section rates between the 323 hospitals (R-square = 0.3725). The first three variables-per cent high parity mothers, per cent labors electronically monitored, and per cent deliveries by obstetricians-together account for about 30 per cent of the variance. This intermediate result indicates that fetal monitoring is positively correlated with an increased cesarean section rate, even after accounting for an inverse measure of maternal need (percentage parity five or greater) as well as the higher number of obstetrician-assisted deliveries usually associated with monitoring. The Kaiser ownership variable, entering with a negative coefficient in the fourth step, suggests that prepayment has an independent attenuating impact on the rate of surgical inTable 5-Study Variables Entering in Final CSR Stepwise Regression Equation Step
Regression
Entered
Variable
Coefficient
0 1 2 3
Intercept Para5 Monitor
-0.988
4 5 6
Kaiser Older White
Ob/Gyn
Signific4nce Level of Coefficient
9.609
0.037 0.024
-2.965
0.0001 0.0001 0.0001
0.0001
0.558 0.027
0.0001 0.0238
AJPH September 1979, Vol. 69, No. 9
Study Para5
Kaiser
Correlation Coefficient
Level of Significance
-0.371 -0.333 -0.296 -0.283 -0.228 -0.212 -0.198 -0.137
0.0001 0.0001 0.0001 0.0001 0.0001 0.0001 0.0003 0.0136
tervention. Holding other factors constant, Kaiser hospitals as a group have a CSR that is about three percentage points
lower than all non-Kaiser hospitals. These results raise questions regarding the relationship between SMR, CSR, and other hospital factors. Since the purpose of the remaining anaylsis is to study the variation of adjusted perinatal mortality rates according to hospital characteristics, the maternal age-parity and newborn factors described in Table 2 are not used in this context. The strongest correlation observed is a negative one between SMR and CSR (Table 6). There is also a significant negative correlation between SMR and the percentage monitored. Other variables negatively correlated with SMR include presence of a neonatal intensive care unit, private nonprofit ownership, and per cent white non-Spanish births. Variables positively correlated with SMR include local government ownership, per cent deliveries by generalists, per cent Spanish surname mothers, and per cent mothers having no prenatal care. These correlations are consistent with the CSR-
Table 6-Correlation Coefficients between Study Variables and Standardized Mortality Ratio (SMR) Study Variable
Correlation Coefficient
Level of Significance
Black CSR District Federal General Illegitimate Kaiser Local Monitor NICU Noprenatal Nonprofit Ob/Gyn Peristudy Profit Spanish Teaching University White
-0.001 -0.329 -0.007 -0.049 0.143 0.099 0.058 0.196 -0.172 -0.136 0.126 -0.146 -0.096 -0.025 0.059 0.302 -0.102 -0.129 -0.250
0.9823 0.0001 0.9020 0.3802 0.0104 0.0741 0.2998 0.0004 0.0019 0.0141 0.0239 0.0084 0.0839 0.6536 0.2917 0.0001 0.0656 0.0206 0.0001
867
WILLIAMS AND HAWES TABLE 7-Mean Values of Selected Variables for Study Hospitals by Grouped Cesarean Section Rate' Cesarean Section Rate (CSR)
Variable
General Ob/Gyn Monitor SMR Number of Hospitals
0.0-4.9
5.0-9.9
10.0-14.9
15.0-19.9
20.0-24.9
25+
Total
(%)
(%)
(%)
(%)
(%)
(%)
(%)
59 26 14 108 15
60 25 28 105 37
18 56 46 87 115
17 72 53 84 108
9 79 65 75 44
2 98 65 70 4
23 60 48 88 323
aExample: 15 of the 323 hospitals had CSR < 5% with an average of 59% of deliveries attended by generalists.
related results showing that hospitals which perform fewer cesarean sections tend to have higher SMRs. Table 7 reports the SMR and three technological indicators (General, Ob/Gyn, and Monitor) for hospitals classified according to CSR in five percentage point intervals. It is clear that hospitals with proportionately more technological interventions have lower standardized mortality ratios. The weighted stepwise regression results for SMR are reported in Table 8. Three variables explained 25 per cent of the variance in the standardized indexes. Significant independent negative associations are observed between SMR and cesarean section rate as well as the presence of a neonatal intensive care unit. Additionally, a significant independent positive association exists between SMR and per cent white Spanish births. These results suggest that hospitals disposed toward technology have lower SMRs and, after the degree of technological intervention is accounted for, hospitals having larger proportions of Spanish-surname mothers have higher standardized mortality rates. TABLE 8-SMR Stepwise Regression Models With CSR Included Step Entered
Variable
Regression Coefficient
0 1 2 3
Intercept CSR Spanish NICU
95.322 - 1.281 0.261
-10.939
Significance Level of
Coefficient
0.0001 0.0001 0.0001
With CSR Suppressed
Step Entered
0 1 2 3 4 5
868
Variable
Regression Coefficient
Intercept Spanish
68.734 0.364
NICUJ Kaiser Black General
-10.806 8.241 0.133 0.110
When suppressing the CSR variable, the stepwise procedure shows that "Spanish" and NICU" are once again strongly associated with SMR. In this context, it is important to note that statewide differentials in fetal viability by ethnic group for given birth weights and gestations have already been accounted for in SMR. The entry of the "Spanish" variable into the regression models indicates that hospitals having proportionately more Spanish-surname deliveries tend to provide less effective intra-and post-partum care. The regression results also indicate that, after accounting for a variety of factors, perinatal mortality rates are about 11 per cent lower in hospitals having an NICU than those that do not. With CSR suppressed, several 4dditional variables associated with lower CSRs enter the SMR equation with positive coefficients. It was shown earlier that the cesarean section rate is lower in hospitals having high percentages of deliveries by generalists and in Kaiser owned hospitals. Such hospitals tend to be independently tissociated with higher adjusted perinatal mortality rates when CSR is suppressed from the regression model. Further, while a high CSR is independently correlated with a high proportion of white non-Spanish deliveries (Table 5), a high SMR is associated with the complementary variables, "Black" and "Spanish" (Table 8). Again, hospitals having higher cesarean section rates have lower standardized perinatal mortality ratios.
Signfficance Level of Coefficient 0.0001 0.0002 0.0367 0.0776 0.1011
Discussion The advent of electronic fetal monitoring and the increased rate of cesarean section are said to reduce birth trauma and perinatal mortality.4-5 " If all births are to benefit from such practices, it is important to determine the distribution of their use. Also, in view of the rapid increase in cesarean section rates, some conclusion must be drawn as to the optimum level. This analysis revealed significant correlations between cesarean section rates and a number of maternal and hospital factors. Based on current modes of obstetric practice, many of the observed associations were as anticipated, yet others raised questions concerning the equity of access to modern obstetrical procedures. While the increase in CSR in primiAJPH September 1979,
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CESAREAN SECTION AND PERINATAL MORTALITY
parous mothers and in older primiparas might be expected on the basis of maternal risk considerations, the lower rates for hospitals serving greater proportions of Spanish-surname mothers, mothers having no prenatal care, out-of-wedlock and adolescent mothers is perplexing. Perhaps the medical need for a cesarean delivery is lower for such mothers, yet it is also possible that hospitals associated with high proportions of these patient types may have lagged in utilizing modern obstetric technology. By most measures of maternal and newborn risk, such patients are likely to require more sophisticated obstetric services, but in fact receive proportionately fewer cesareans. This result suggests a potential misallocation of medical resources. Similarly, it was surprising to find the two newborn variables, low birth weight and multiple births, not significantly correlated with CSR. In the case of multiple births, this result may be due to little variation between hospitals for that variable since the occurrence of multiple births is likely to be uniformly distributed. Most of the hospital variables indicative of the level of sophistication of obstetrical practice are significantly correlated with the cesarean rate, and some of these variables continue to display independent associations in the multiple regression results. These findings suggest that increasing cesarean rates are the medical profession's response to yet another "technological imperative"23 which was stimulated by the advent of fetal monitoring. The hospital ownership variables are central to understanding the impact of organized medical care services on the utilization of technological advances. The significant negative coefficient for Kaiser ownership in the CSR regression equation confirms the notion prepaid health care financing tends to have an independent attenuating effect on the rate of surgical interventions. Whether the lower rates are optimal or uiot is yet another question. Also, it is possible that the maternal risk characteristics may be different for patients served by Kaiser hospitals and that the regression equation in Table 5 does not adequately adjust for such characteristics. Overall, the results suggest those variables associated with a high cesarean section rate in hospitals, perhaps even cesarean section itself, may have a beneficial effect on perinatal outcomes. That is, hospitals with higher cesarean section rates, higher rates of fetal monitoring, higher proportions of obstetrician-attended deliveries, and the availability of neonatal intensive care have better perinatal outcomes. In summary, hospitals with a high degree of technological intervention have lower standardized perinatal mortality rates. There are, however, some important caveats. First, the SMR as presently defined accounts only for the condition of the newborn at the time of birth, and is not capable of adjusting for the possibility of iatrogenic prematurity. While each newborn's birth weight and gestational age are accounted for, it may be possible that a very high percentage of elective cesareans could tend to lower weight and gestation by causing a significant number of premature deliveries. However, as shown in Table 9, this does not seem to have occurred on a statewide basis since the expected perinatal mortality rate has been slowly declining. On the other hand, the observed AJPH September 1979, Vol. 69, No. 9
TABLE 9-Trends in Observed, Expected, and Standardized Perinatal Mortality Rates: California 1970-1977 Observed Perinatal Mortality Ratea
Expected Perinatal Mortality Rateb
Standardized Perinatal Mortality Ratioc
1970
21.3
1971 1972 1973 1974 1975 1976
20.1
18.9 18.1 18.2 18.2 17.8 17.8 17.7 17.4
112.9 110.5 105.7 98.8 95.3 89.1 86.9 81.3
Year
1977
19.2 17.9 17.0 15.8 15.4 14.2
aExcludes births of less than 500 g and those with unknown birth weights. bBased on statewide perinatal mortality rates for combined 1970-1976 birth cohorts.
CSMR =
100 x (observed rate . expected
rate).
rate has declined much more rapidly, thus yielding a 30 per cent decrease in SMR from 1970 through 1977. Second, the positive association between cesarean section rates and improved perinatal outcomes does not demonstrate a causal link between cesarean section and perinatal outcome for a given pregnancy. Hospitals performing proportionately more cesarean deliveries also have more specialized staffs and equipment, and a high cesarean section rate may be just an indicator for careful, sophisticated ob-
stetrical practice. Further, this study, while based on a large aggregate of births, focused on a single year and did not measure the impact of technological change over time. Third, the outcome measure used here does not address the issue of maternal morbidity and mortality. Even if a causal link between electronic monitoring, cesarean deliveries, and improved perinatal outcomes could be demonstrated, the question of increased maternal risks still remains.'3' '5 While the purpose of this analysis was to measure the effects of these technologies on mortality, there are other important considerations in the childbearing process that may be adversely affected by such interventions. Fourth, it is possible that improved perinatal outcomes could be achieved by other means. For example, programs for better prenatal nutrition to improve birth weight, and for ameliorating the ill effects of adolescent and out-of-wedlock pregnancies might achieve comparable savings in terms of actual perinatal loss. Finally, the increased costs of this technical approach to childbirth have not been discussed. These costs include not only the more intensive use of medical resources and increased lengths of stay, but also decreased maternal function following hospital discharge. Other indirect costs include the rising number of repeat cesarean sections resulting from the increased primary rate. With these caveats in mind, we cannot conclude that the current emphasis on technology in obstetrics is justified. However, the statistical results suggest that hospitals which use a greater proportion of technological interventions and have available sophisticated manpower and equipment do have better perinatal outcomes. 869
WILLIAMS AND HAWES
REFERENCES 1. Petitti D, Olson RO, Williams RL: Cesarean section in California: 1960-1975. Am J Obstet Gynecol 133:391-397, 1979 2. Lowe JA, Klassen DF, Loup RJ: Cesarean sections in U.S. PAS hospitals. PAS Reporter 14:1, 1976. 3. Johnell HE, Ostberg, H, Wahlstrand T: Increasing cesarean section rate. Acta Obstet Gynecol Scand 55:95-100, 1976. 4. Amato JC: Fetal monitoring in a community hospital. Obstet Gynecol 50:269-274, 1977. 5. Evrard JR, Gold EM: Cesarean section: risk/benefit. Perinatal Care 2:4-10, 1978. 6. Haverkamp HD, Thompson, HE, McFee JG, et al: The evaulation of continuous fetal heart monitoring in high risk pregnancy. Am J Obstet Gynecol 125:310-320, 1976. 7. Hibbard LT: Changing trends in cesarean section. Am J Obstet Gynecol i24:798-804, 1976. 8. Hughey MJ, LaPata RE, McElin TW, et al: The effect of fetal monitoring on the incidence of cesarean section. Obstet Gynecol 49:513-518, 1977. 9. Tutera G, Newman RL: Fetal monitoring: its effect on perinatal mortality and cesarean section rates and its complications. Am J Obstet Gynecol 122:750-754, 1975. 10. Neutra RR, Fienberg SE, Greenland S, et al: Effect of fetal monitoring on neonatal death rates. N Engl J Med 299:324-326, 1978. 11. Paul RH, Hon EH: Clinical fetal monitoring: effect on perinatal outcome. Am J Obstet Gynecol 118:529-533, 1974. 12. Baker RA: Technological Intervention in Obstetrics: has the pendulum swung too far? Obstet Gynecol 51:241-244, 1978. 13. Green SL, Sarubbi FA: Risk factors associated with post cesarean section febrile morbidity. Obstet Gynecol 49:686-690, 1977. 14. Hack M, Fanaroff AA, Klaus MH, et al: Neonatal respiratory distress following elective delivery: a preventable disease? Am J Obstet Gynecol 126:43-47, 1976.
15. Hagen D: Maternal febrile morbidity associated with fetal monitoring and cesarean section. Obstet Gynecol 46:260-262, 1975. 16. Maisels MJ, Rees R, Marks K, et al: Elective delivery of the term fetus: an obstetrical hazard. JAMA 238:2036-2039, 1977. 17. Reed DM, Bakketeig LS, Nugent RP: The epidemiology of respiratory distress syndrome in Norway. Am J Epidemiol 107:299-310, 1978. 18. Armitage P: Statistical Methods in Medical Research. Oxford: Blackwell, 1971. 19. Williams RL: Measuring the effectiveness of perinatal medical care. Medical Care 17:95-110, 1979. 20. Barr AJ, Goodnight JH, Sall JP, et al: A User's Guide to SAS 76. Raleigh: SAS Institute, 1976. 21. Buse A: Goodness of fit in generalized least squares estimation. Am Stat 27:106-108, 1973. 22. LaDou J, Likens JD: Medicine and Money. Cambridge: Ballinger, 1977. 23. Fuchs VR: Who Shall Live? New York: Basic Books, 1974.
ACKNOWLEDGMENTS Supported in part in Maternal and Child Health Grant No. MCR-060390-03 from the Bureau of Community Health Services, DHEW. This study was performed in cooperation with the staff of the Maternal and Child Branch of the California Department of Health Services. The authors are indebted to Diana Petitti and Mich Tashiro for a number of valuable contributions. Helpful comments on earlier drafts were received from Joseph Brazie, Siegried Centerwall, George Cunningham, Lyn Headley, Russell Laros, Frank Norris, and Roderic Phibbs. William Mason assisted in processing the sample data.
APHA 107th Annual Meeting
Epildemiologic Exchange
Deadline for Abstracts is October 1 The Epidemiology Section of the American Public Health Association will again sponsor the annual Epidemiologic Exchange on Wednesday, November 7, 1979, from 2pm to 5pm, during the APHA Annual Meeting in New York City. The session will be held at the Sheraton Centre, Princess Room. Abstracts are now being invited by Dr. Michael B. Gregg, organizer and presider of the session. The deadline for submission of abstracts is October 1. Abstracts should be limited to 200 words; no special abstract form is required. This annual forum presents the latest findings in epidemiologic investigations from around the world. Approximately 12 presentations can be accepted for this symposium. The oral presentations are limited to about 15 minutes each. Papers to be presented at this session will summarize "late-breaking" epidemiologic investigations, studies, and methodologies which have been conceived, conducted, and/or concluded during the last 6-12 months. Send abstracts to: Dr. Michael B. Gregg, Deputy Director, Bureau of Epidemiology, Center for Disease Control DHEW/PHS, Atlanta, GA 30333. Telephone 404/329-3636.
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