Original Article

Hospital of Delivery and the Racial Differences in Late Preterm and Early-Term Labor Induction Karna Murthy, MD, MSc1,2 Michelle Macheras, MS3 Scott A. Lorch, MD, MSCE3

William A. Grobman, MD, MBA4

1 Department of Pediatrics, Ann and Robert H. Lurie Children’s

Address for correspondence Karna Murthy, MD, MSc, Division of Neonatology, Ann & Robert H. Lurie Children’s Hospital of Chicago, 225 East Chicago Avenue, Box #45, Chicago, IL 60611 (e-mail: [email protected]).

Hospital of Chicago, Chicago, Illinois 2 Department of Pediatrics, Feinberg School of Medicine, Northwestern University, Chicago, Illinois 3 Division of Neonatology, Department of Pediatrics, Children’s Hospital of Philadelphia and the Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 4 Division of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois Am J Perinatol 2015;32:952–959.

Abstract

Keywords

► ► ► ► ►

epidemiology induction of labor late preterm early-term vital statistics

Objectives To estimate the interhospital differences in induction of labor (IOL) from 340/7 to 386/7 weeks’ gestation by race/ethnicity. Methods Women between 34 and 42 weeks’ gestation during 1995 and 2009 in three states were identified using linked maternal and infant records. Women with prior cesarean delivery, premature rupture of membranes, gestational hypertension, who delivered at hospitals with < 100 annual births, or who had missing data were excluded. The outcomes were inductions at early-term (ETI: between 370/7 and 386/7 weeks’) and late preterm (LPI: from 340/7–366/7 weeks’) gestations. Cox proportional hazard ratios (HR) were used to estimate the independent associations between race/ethnicity and hospital of delivery on ETI and LPI. Results A total of 6.98 million eligible women delivered at 469 hospitals. ETI and LPI occurred in 3.20 and 0.40% of women, respectively. Non-Hispanic white women (3.99%) received ETI most commonly; conversely, LPI was highest among non-Hispanic black women (0.50%). In multivariable analyses, non-Hispanic black race was protective for ETI (HR ¼ 0.89; p < 0.01) and was a risk factor for LPI (HR ¼ 1.26; p < 0.01) after adjusting for patient factors and the delivery hospital. Conclusion Racial differences in ETI and LPI appear to be pervasive. Much of the unaccounted racial/ethnic variation remains seems secondary to within-hospital differences in selecting women for IOL.

Induction of labor (IOL), both during the late preterm (LPI) and early-term (ETI) periods, has increased dramatically in recent years.1,2 Both the frequency and the magnitude of these increases have been different for women of different races/ethnicities. LPI (from 340/7–366/7 weeks’ gestation) was most frequent and rose most rapidly among black women; conversely, ETI

(from 370/7–386/7 weeks’ gestation) occurred most commonly and had the largest increase among non-Hispanic white (NHW) women.1,2 These increases have occurred despite reports demonstrating that birth before 39 weeks’ gestation is associated with higher frequencies of hospitalization,3 neonatal morbidities,4 and even infant mortality.5

received July 10, 2014 accepted after revision December 15, 2014 published online March 31, 2015

Copyright © 2015 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.

DOI http://dx.doi.org/ 10.1055/s-0035-1544191. ISSN 0735-1631.

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Nevertheless, the precise origin of these differences is uncertain.3 For example, the racial/ethnic differences in LPI and ETI may exist at all hospitals. Alternatively, the practices of LPI and ETI may be more frequent at hospitals that disproportionately serve black and NHW women, respectively. Earlier work suggests that patient, provider, or institutional factors are related to IOL before 39 weeks’ gestation,6 although what these factors may be, the magnitude of their effect, and their relationship to race/ethnicity are undetermined.7 Moreover, these increases in LPI and ETI have occurred in the context of consistent recommendations that only medical indications should result in IOL at less than 39 weeks’ gestation.3,6,8 Whether providers within individual hospitals have different thresholds to induce and whether these thresholds are differentially related to maternal race/ ethnicity remains uncertain.3,6 We hypothesized that racial/ethnic differences in LPI and ETI would significantly vary between hospitals, and these interhospital differences would explain the observed racial/ ethnic discrepancies in the overall rates of LPI and ETI. Thus, the aim of this study was to estimate the variation of LPI and ETI both between delivery hospitals and within delivery hospitals as a function of maternal race/ethnicity.

Methods We obtained birth certificate data linked with maternal hospitalization records on all women who had live-born deliveries occurring in California, Missouri, and Pennsylvania between January 1, 1995 and June 30, 2009.9 These states were chosen given the combination of adequate data availability, sufficient delivery volume, and geographic and racial/ ethnic diversity. Probabilistic methods were applied to link birth certificates with maternal/infant hospitalization records using hospital identifiers, birth date, sex, cesarean delivery, maternal/infant zip code, payor source, and race/ ethnicity.10 In a second step for unmatched records, health status codes were used to link infants in the two datasets. Overall, 98.5% of the records were linked, and 80% of the remaining unmatched records had a missing code for the delivery hospital, which suggested that birth occurred outside of a hospital.10 These records were excluded from further study. Among matched records, data from women/infants were also excluded if birth weight was less than 400 g or greater than 8 kg, or if the birth weight was more than 5 standard deviations from the mean birth weight for gestational age because of concerns that either birth weight or gestational age was miscoded.9–13 The Institutional Review Boards of the California, Missouri, and Pennsylvania Departments of Health and the Children’s Hospital of Philadelphia approved this study. Women between 34 and 42 weeks’ gestation with nonanomalous live-born neonates were identified for this study. Women for whom IOL was unlikely or contraindicated (i.e., prior cesarean deliveries, non-vertex presentation, placenta previa, etc.) or whose IOL could not have been planned in the outpatient setting (i.e., due to no prenatal care) were exclud-

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ed. Also, excluded were those women whose database records could not be used to determine race/ethnicity, gestational age at birth, hospital of delivery, or type of labor initiation, given that the main exposures (i.e., race/ethnicity, hospital of delivery) and the primary outcomes (i.e., LPI and ETI) could not be determined. In addition, women with pregnancyinduced hypertension or with premature preterm rupture of membranes (pPROM) were not included, given that these conditions may develop as the pregnancy progresses. However, because the timing of onset and severity of these conditions were unknown, these variables could not be used to risk-adjust when estimated gestational age at delivery was embedded in the primary outcome.1,2 Women with preterm labor were also omitted, as their initiation of labor was spontaneous. Of note, pPROM and preterm labor were ascertained using administrative codes (Appendix 1) in the maternal inpatient record.14 Finally, women whose birth hospital had less than 100 annual deliveries were omitted given the imprecision of estimates associated with low number of births at the specific hospital. LPI and ETI (yes/no) were the main outcomes of this analysis and were defined as IOL (procedure code 73.4) between 340/7–366/7 and 370/7–386/7 weeks’ gestation, respectively. The gestational age at birth was derived from the birth certificate based on the field that codes for the best clinical estimate of gestational age. Women who had labor augmentation were considered not to have undergone labor induction. Maternal race and ethnicity were self-reported in the birth certificate data and classified into four categories: NHW, non-Hispanic black, Hispanic, and “other,” based on information in the maternal hospital discharge record in each state. Hospital of delivery was captured from this discharge record and validated using birth certificate records. Other independent, patient-level variables were used to adjust for case-mix and grouped into categories based on previous work.11 Socioeconomic factors included maternal insurance status, education, trimester of prenatal care initiation, and maternal age identified from birth certificate data. Referent to women from 20 to 34 years old, maternal age was categorized into teen pregnancy (age  19) and advanced maternal age (age  35). Maternal antenatal conditions that included chronic hypertension, thyroid disease, urinary tract infection, maternal heart disease, renal disease, and diabetes mellitus were identified using codes (Supplementary Digital Content: Appendix 1) from both the birth certificate and the maternal/infant hospital discharge data. Although labor induction is initiated before ascertaining the infant’s birth weight, small for gestational age less than 10th percentile15 was considered as a variable that may indicate a medically indicated IOL for fetal growth restriction, and as such, was adjusted for in the regression analyses. Bivariable analyses were performed using Student t-test, analysis of variance (ANOVA) and χ2, as appropriate, to determine the characteristics that were significantly associated with IOL and race/ ethnicity. To quantify the interhospital variability in IOL, the frequencies of LPI and ETI were calculated for each racial/ethnic group during the study period. All women who delivered American Journal of Perinatology

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between 340/7 and 426/7 weeks’ gestation were included in denominator for LPI, and all women who delivered between 370/7 and 426/7 weeks’ gestation were included in the denominator for ETI. Descriptive data are reported including the mean, median, and the distribution of these rates. For each factor or set of factors, multivariable Cox proportional hazards regression models were used to estimate the association between race/ethnicity and either LPI or ETI. In these equations, the duration of pregnancy served as the time variable for the models. The association of maternal race/ ethnicity with IOL was first estimated in univariable analysis and then in a series of multivariable equations after adjustment with potential confounding factors. Each sequential model introduced another set of factors in the following order: race/ethnicity (Model A); other socioeconomic and demographic factors (Model B); antenatal complications of pregnancy (Model C); and small-for-gestational-age birth weight (Model D). Changes to the coefficients on race/ethnicity in subsequent models suggest that the addition of these factors explains some of the unadjusted differences in LPI or ETI between racial/ethnic groups. For all multivariable analyses, the referent group was NHW women because they received IOL most frequently at  39 weeks’ gestation. Even if overall racial/ethnic differences in the frequency of LPI and ETI are present, it is uncertain whether these differences exist at all hospitals or are due to higher frequencies at hospitals where women of unlike races/ethnicities differentially receive care. Thus, we completed an analysis where the year of birth and then the hospital of delivery were introduced as a fixed effect (Model E).

Using this conceptual framework and approach, we sought to understand whether two patients who deliver at the same hospital but differ only by race/ethnicity have a different chance of IOL. This was determined by assessing the change in the coefficient of race/ethnicity on IOL between Model D, which included all patient-level confounding variables, and Model E, which added the variable coding for delivery hospital to the models. Any residual and significant associations between race/ethnicity and LPI or ETI suggest that other factors within-hospital may explain these differences. This framework is similar to other studies.11,16,17 Given the large sample sizes, significance was defined as p < 0.01 to reduce the chance of obtaining falsely positive results. Statistical tests were two-tailed, and the analyses were completed using SAS 9.3 (Cary, NC).

Results From 1995 to 2009, there were 9,726,499 women who gave birth in the three states (California 75.8%; Missouri 8.62%; and Pennsylvania 15.58%); 760,885 (7.82%) women delivered in the late preterm period and 2,567,445 (26.40%) delivered in the early-term period. After restricting the population of gravid women to those who met the inclusion criteria, 6,980,425 and 6,731,376 women were eligible for the LPI and ETI analyses, respectively (►Table 1). LPI occurred in 0.40% of eligible women; among the women who delivered in the late preterm period, 11.2% received LPI. This proportion rose by 67% during the 15-year study period (8.17% of late preterm births in 1995

Table 1 Inclusion and exclusion criteria for the study population (1995–2009) Late preterm

Early term

N

%

N

%

9,726,499

100

8,965,614

100

Multiple gestation

212,201

2.18

115,612

1.29

2

Maternal age  12 OR  50 y

1,204

0.01

974

0.01

3

Prior cesarean delivery

1,344,627

13.82

1,228,363

13.70

4

Non-vertex/breech presentation

295,551

3.04

246,106

2.74

5

Premature rupture of membranes

429,621

4.42

322,784

3.60

6

No prenatal care

42,815

0.44

35,112

0.39

7

Unknown race/ethnicity

107,687

1.11

100,725

1.12

8

Pregnancy-induced hypertension

289,594

2.98

218,382

2.44

9

Preterm labor

495,849

5.10

155,236

1.73

10

Placental previa

49,555

0.51

35,096

0.39

11

Disorders of placentation

117,266

1.21

83,935

0.94

12

Eclampsia

6,954

0.07

5,166

0.06

6,980,873

71.77

6,731,376

75.08

Exclusion characteristics 1

Women eligible for the analysis (from maternal ICD-9) a

Late preterm induction (LPI) analysis identified gravid women at 34 weeks’ gestation; early-term induction (ETI) analysis identified women still pregnancy at 37 weeks’ gestation. A total of 448 and 426 women were excluded in the LPI and ETI analysis, respectively, because they delivered at hospitals with  100 annual deliveries.

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to 13.69% in 2009, p < 0.01). ETI, which occurred in 3.2% of all eligible women, was initiated in 13.36% of those delivering in the early-term period. This proportion increased by 62% during the study period (9.27% of early term births in 1995 to 15.03% in 2009, p < 0.01). Stratified by maternal race/ethnicity, the distribution of individual hospital rates of both LPI and ETI is demonstrated in ►Fig. 1. The frequencies of both LPI and ETI significantly varied between the included hospitals. ►Table 2 depicts the comparisons in the characteristics of the eligible population stratified by maternal race/ethnicity. Non-Hispanic black women were more likely to be younger and unmarried, and to have chronic hypertension and diabetes mellitus. These women were also most likely to undergo LPI (hazard ratio [HR] ¼ 1.39, 99% confidence interval [CI] [1.32, 1.47]). Multivariable analyses demonstrated that the association of non-Hispanic black race with LPI persisted even after the addition of socioeconomic factors, antenatal and medical complications, year of birth, and then hospital of birth as a fixed effect (HR ¼ 1.26; 99% CI [1.18, 1.34]; ►Table 3). Of note,

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Fig. 1 Box plot of hospital rates of LPI (white) and ETI (gray) stratified by race/ethnicity. Triangles represent the mean racial/ethnic-specific rates of LPI or ETI. ETI, early-term induction; LPI, late preterm induction.

Table 2 Maternal characteristics stratified by race/ethnicity Variable

NHW

Hispanic

Black

Other

All

N

3,260,068

2,422,363

523,566

774,876

6,980,873

%

46.7

34.7

7.5

11.1

100

28.2  6.0

25.8  6.0

25.0  6.1

29.4  5.7

27.3  6.2

Age < 18 y

2.53

5.94

7.83

1.82

4.03

Age 36–49 y

12.17

7.22

6.77

14.46

10.30

1.13

1.09

0.90

1.16

1.10

No high school

1.42

21.38

1.38

4.65

8.71

Some high school

9.65

28.65

20.66

7.96

16.88

Maternal age, y

Uninsured Education

Some college

59.08

19.94

37.95

63.76

44.43

Unknown

1.33

1.94

2.27

2.48

1.74

Chorioamnionitis

4.00

3.87

5.85

5.31

4.24

UTI

1.47

1.18

2.65

0.97

1.40

Maternal kidney disease

0.12

0.09

0.15

0.08

0.11

Thyroid disease

1.49

0.56

0.58

1.22

1.07

Antenatal conditions

Chronic hypertension

0.72

0.36

1.47

0.52

0.63

Diabetes mellitus

0.40

0.57

0.62

0.49

0.48

Gestational diabetes

3.36

4.47

2.89

0.49

4.05

Nulliparous

46.22

39.69

43.12

50.25

44.17

SGA (< 10th%ile)

6.33

7.32

13.12

10.30

7.62

LPI

0.36

0.45

0.50

0.36

0.40

3.99

2.32

3.15

2.68

3.20

ETI

a

Abbreviations: ETI, early-term induction of labor; LPI, late preterm induction of labor; NHW, non-Hispanic white; SGA, small for gestational age; UTI, urinary tract infection. a Restricted calculation for the women delivering at  37 weeks’ gestation only. All data presented as mean  standard deviation or %. American Journal of Perinatology

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Table 3 Multivariable Cox proportional hazards regression analyses demonstrating the association between racial/ethnic groups and either LPI or ETI (with a referent group of NHW women) Model

Description

A

Race/ethnicity Non-Hispanic blackb b

1.32

99% CI

1.47

0.82

0.80

0.83

1.22

1.31

0.60

0.59

0.61

1.05

0.69

0.68

0.70

Non-Hispanic blackb

1.36

1.31

1.42

0.85

0.83

0.87

Hispanic ethnicityb

1.21

1.17

1.24

0.66

0.65

0.67

1.0

0.96

1.04

0.69

0.67

0.70

Non-Hispanic blackb

1.24

1.18

1.29

0.80

0.78

0.81

Hispanic ethnicityb

1.16

1.12

1.19

0.64

0.63

0.65

Other race/ethnicity

0.97

0.93

1.01

0.66

0.65

0.67

1.24

1.19

1.30

0.79

0.77

0.81

1.16

1.12

1.19

0.64

0.63

0.65

0.97

0.93

1.01

0.65

0.64

0.66

1.26

1.18

1.34

0.89

0.87

0.91

0.91

0.88

0.96

0.72

0.71

0.73

0.79

0.75

0.84

0.69

0.68

0.71

þ Socioeconomic and demographic variables

þ Antenatal conditions

a

þ SGA (< 10th percentile) Non-Hispanic blackb Hispanic ethnicity

b

Other race/ethnicity E

1.39

HR

0.94

Other race/ethnicity

D

99% CI

1.26

Other race/ethnicity

C

HR

1.0

Hispanic ethnicity B

ETIb

LPI

þ Hospital of delivery and year of birth Non-Hispanic blackb Hispanic ethnicity

b

Other race/ethnicity

b

Abbreviations: CI, confidence interval; ETI, early-term induction; HR, hazard ratio; LPI; late preterm induction, NHW, non-Hispanic white; SGA, small for gestational age. Note: SGA based on Alexander et al.15 a Includes preterm labor, chronic hypertension, thyroid disease, urinary tract infection, maternal heart disease, renal disease, and diabetes mellitus. b P < 0.001.

the addition of hospital of delivery changed the magnitude of the association between non-Hispanic black race and LPI by only 2%. Conversely, for Hispanic women, the inclusion of hospital of delivery had a dramatic effect on the association of ethnicity with LPI: after accounting for the hospital of delivery, Hispanic women were less likely to experience LPI (HR ¼ 0.91, 99% CI: 0.88–0.96), while without this adjustment, Hispanic ethnicity was a significant risk factor for experiencing LPI (►Table 3). In contrast, ETI was most common in NHW women, with both non-Hispanic black and Hispanic women being significantly less likely to experience an ETI (HR ¼ 0.82, 99% CI [0.80, 0.83]; HR ¼ 0.60, 99% CI [0.59, 0.61], respectively). The racial/ethnic difference in ETI persisted even after the sequential addition of the potential confounding factors (nonHispanic black: HR ¼ 0.89, 99% CI [0.87, 0.91]; Hispanic: HR ¼ 0.71, 99% CI [0.71, 0.73]). The addition of delivery hospital changed the magnitude of the association between non-Hispanic black race and ETI by 12% (►Table 3) and between Hispanic ethnicity and ETI by only 6%. American Journal of Perinatology

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Discussion This study demonstrates that both of the frequencies of LPI and ETI were associated with maternal race/ethnicity for women delivering in three states during a recent 15-year period. The observed differences persisted even after accounting for patient characteristics, as well as for hospital of delivery, which minimally contributed to the observed differences in rates of IOL, in general. Specifically, for nonHispanic black women, the differences in IOL appear pervasive and not primarily related to differences in care at particular hospitals.1,2,18 The findings were similar for Hispanic women in the setting of ETI. Conversely, the hospital of delivery appeared to explain the variations in LPI, suggesting that hospitals that deliver Hispanic women more frequently are generally more likely to initiate LPI in their population. Previous work has demonstrated racial/ethnic differences in the provision of IOL between 340/7 and 386/7 weeks’ gestation, and the current analysis builds on these published works.19 In those national analyses, black race/ethnicity was

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racial/ethnic differences. For example, factors such as providers’ and/or patients’ attitudes and beliefs may be responsible, and these practices were unmeasured in this cohort. However, because it appears that the racial/ethnic differences in IOL are widespread, further study should focus whether a potential source of the disparity is related to providers’ practices, patient preferences, or the interactions between them. Most importantly, IOL is merely a process measure, and the degrees to which these reported differences are associated with disparities in maternal and perinatal outcomes remain uncertain.4,31,32 Further research will need to investigate the underlying variations among obstetric providers and patients that have led to the increase in and the racial/ethnic differences in LPI and ETI and the differences in outcome that may occur as a consequence of these disparate practices.

Conflict of Interest None of the authors have a conflict of interest to disclose.

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differences in late preterm induction. Am J Obstet Gynecol 2011; 205(5):458.e1–458.e7 Murthy K, Grobman WA, Lee TA, Holl JL. Trends in induction of labor at early-term gestation. Am J Obstet Gynecol 2011;204(5): 435.e1–435.e6 Gyamfi-Bannerman C, Fuchs KM, Young OM, Hoffman MK. Nonspontaneous late preterm birth: etiology and outcomes. Am J Obstet Gynecol 2011;205(5):456.e1–456.e6 Hibbard JU, Wilkins I, Sun L, et al; Consortium on Safe Labor. Respiratory morbidity in late preterm births. JAMA 2010;304(4): 419–425 MacDorman MF, Declercq E, Zhang J. Obstetrical intervention and the singleton preterm birth rate in the United States from 19912006. Am J Public Health 2010;100(11):2241–2247 Spong CY, Mercer BM, D’alton M, Kilpatrick S, Blackwell S, Saade G. Timing of indicated late-preterm and early-term birth. Obstet Gynecol 2011;118(2 Pt 1):323–333 Moore J, Low LK. Factors that influence the practice of elective induction of labor: what does the evidence tell us? J Perinat Neonatal Nurs 2012;26(3):242–250 Koopmans CM, Bijlenga D, Groen H, et al; HYPITAT study group. Induction of labour versus expectant monitoring for gestational hypertension or mild pre-eclampsia after 36 weeks’ gestation (HYPITAT): a multicentre, open-label randomised controlled trial. Lancet 2009;374(9694):979–988 Lorch SA, Srinivas SK, Ahlberg C, Small DS. The impact of obstetric unit closures on maternal and infant pregnancy outcomes. Health Serv Res 2013;48(2 Pt 1):455–475 Herrchen B, Gould JB, Nesbitt TS. Vital statistics linked birth/infant death and hospital discharge record linkage for epidemiological studies. Comput Biomed Res 1997;30(4):290–305 Lorch SA, Kroelinger CD, Ahlberg C, Barfield WD. Factors that mediate racial/ethnic disparities in US fetal death rates. Am J Public Health 2012;102(10):1902–1910 Parker JD, Schoendorf KC. Implications of cleaning gestational age data. Paediatr Perinat Epidemiol 2002;16(2):181–187 Lorch SA, Baiocchi M, Ahlberg CE, Small DS. The differential impact of delivery hospital on the outcomes of premature infants. Pediatrics 2012;130(2):270–278 American Journal of Perinatology

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independently associated with LPI and inversely related to ETI; however, hospitals of delivery were not assessed.1,2 Here, the selected states are populated by women from diverse sets of communities and include urban, rural, and racially/ethnically diverse populations.11 Also, the linkage between birth certificate and maternal discharge records increases the sensitivity to ascertain diagnoses and complications that the birth certificate registry alone may omit. In addition, whereas other studies have focused on IOL at term, this analysis focuses on IOL from 340/7 to 386/7 weeks’ gestation, a period in pregnancy in which IOL should be avoided unless an unequivocal medical indication exists.20,21 Moreover, this analysis incorporates hospital as a fixed effect in the regression equation, which allows clarification that the racial/ethnic discrepancies were largely unrelated to interhospital differences in care. Of note, the racial/ethnic differences in LPI and ETI do not parallel the observed variation in stillbirth. In the late preterm period, non-Hispanic black women are approximately 60% more likely to experience stillbirth compared with NHW women, and in that regard, these results support the concept that one reason that LPI is performed is to avoid stillbirth in at-risk women.22,23 Yet, NHW women after 37 weeks’ gestation receive IOL most frequently, even though black women continue to remain at the highest risk for stillbirth. Further work is needed to explore the underlying relationship between maternal race/ethnicity, IOL, and stillbirth to determine the optimal criteria for the selection of women who are at risk for having a stillbirth24 and who may avert this outcome by receiving either LPI or ETI. There were several limitations to this study. Maternal race/ ethnicity was classified into four categories and does not fully represent the racial/ethnic diversity of the gravid population.25 This is especially true for the classification of women as being of “other” race/ethnicity, a category that encompasses women from multiple backgrounds. As in any analysis of secondary data, unknown and unmeasured factors (e.g., fetal lung maturity, severity of antenatal complications)20,21 could have modified the observed associations. Also, it was not possible to determine whether women received elective IOL; however, for women delivering from 34 to 38 weeks’ gestation, elective IOL was consistently unsupported by national practice recommendations.20,21 Moreover, coding errors may have occurred, such that women may have been misclassified as to whether they received an induction.26–28 There were likely low-frequency conditions that reasonably serve as indications for IOL (e.g., isoimmunization)6,29 however, many were considered with either exclusion criteria or as covariates, and for those that were not, their low frequencies after stratifying by maternal race/ethnicity are unlikely to nullify the observed associations.29 Nevertheless, the Centers for Disease Control and Prevention and numerous previous investigators have used these data to examine national trends in IOL for both mothers and infants.25,30 Linkage of birth certificate records with maternal discharge information increases the sensitivity of capturing maternal diagnoses and interventions.10,27 This study cannot capture or determine all the factors contributing to the rise in IOL between 340/7 and 386/7 weeks’ gestation and the origins of these persisting

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14 Srinivas SK, Fager C, Lorch SA. Evaluating risk-adjusted cesarean

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delivery rate as a measure of obstetric quality. Obstet Gynecol 2010;115(5):1007–1013 Alexander GR, Himes JH, Kaufman RB, Mor J, Kogan M. A United States national reference for fetal growth. Obstet Gynecol 1996; 87(2):163–168 Victora CG, Huttly SR, Fuchs SC, Olinto MT. The role of conceptual frameworks in epidemiological analysis: a hierarchical approach. Int J Epidemiol 1997;26(1):224–227 Baker D, Taylor H, Henderson J; ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood. Inequality in infant morbidity: causes and consequences in England in the 1990s. J Epidemiol Community Health 1998;52(7):451–458 Glantz JC. Obstetric variation, intervention, and outcomes: doing more but accomplishing less. Birth 2012;39(4):286–290 Murthy K, Grobman WA, Lee TA, Holl JL. Racial disparities in term induction of labor rates in Illinois. Med Care 2008;46(9): 900–904 ACOG Committee on Practice Bulletins – Obstetrics. ACOG Practice Bulletin No. 107: Induction of labor. Obstet Gynecol 2009;114(2 Pt 1):386–397 American Congress of Obstetricians & Gynecologists (ACOG) Committee on Practice Bulletins. ACOG Committee Opinion no. 561: Non-Medically Indicated Early-Term Deliveries. Obstet Gynecol 2013;121(4):911–915 Willinger M, Ko CW, Reddy UM. Racial disparities in stillbirth risk across gestation in the United States. Am J Obstet Gynecol 2009; 201(5):469.e1–469.e8

stillbirth throughout pregnancy in the United States. Am J Obstet Gynecol 2006;195(3):764–770 Aghideh FK, Mullin PM, Ingles S, et al. A comparison of obstetrical outcomes with labor induction agents used at term. J Matern Fetal Neonatal Med 2014;27(6):592–596 Kochanek KD, Kirmeyer SE, Martin JA, Strobino DM, Guyer B. Annual summary of vital statistics: 2009. Pediatrics 2012;129(2):338–348 Reichman NE, Schwartz-Soicher O. Accuracy of birth certificate data by risk factors and outcomes: analysis of data from New Jersey. Am J Obstet Gynecol 2007;197(1):32.e1–32.e8 Baumeister L, Marchi K, Pearl M, Williams R, Braveman P. The validity of information on “race” and “Hispanic ethnicity” in California birth certificate data. Health Serv Res 2000;35(4):869–883 Roohan PJ, Josberger RE, Acar J, Dabir P, Feder HM, Gagliano PJ. Validation of birth certificate data in New York State. J Community Health 2003;28(5):335–346 Chauhan SP, Ananth CV. Induction of labor in the United States: a critical appraisal of appropriateness and reducibility. Semin Perinatol 2012;36(5):336–343 Hoyert DL, Freedman MA, Strobino DM, Guyer B. Annual summary of vital statistics: 2000. Pediatrics 2001;108(6):1241–1255 Bailit JL, Gregory KD, Reddy UM, et al. Maternal and neonatal outcomes by labor onset type and gestational age. Am J Obstet Gynecol 2010;202(3):245.e1–245.e12 Stock SJ, Ferguson E, Duffy A, Ford I, Chalmers J, Norman JE. Outcomes of elective induction of labour compared with expectant management: population based study. BMJ 2012;344:e2838

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Appendix 1 ICD-9 codes utilized for antenatal/fetal conditions PTL

CH

Thyroid disease

UTI

Heart disease

Renal disease

Diabetes mellitus

644.0

642.0

648.1

599.0

648.5

646.2

250

644.00

642.00

648.10

646.6

648.50

646.20

250.0

644.03

642.01

648.11

646.60

648.51

646.21

250.00

644.2

642.02

648.12

646.61

648.52

646.22

250.01

644.20

642.03

648.13

646.62

648.53

646.23

250.02

644.21

642.04

648.14

646.63

648.54

646.24

250.03

642.1

646.64

250.1

642.10

250.10

642.11

250.11

642.12

250.12

642.13

250.13

642.14

250.2

642.2

250.20

642.20

250.21

642.21

250.22

642.22

250.23

642.23

250.3

642.24

250.30 250.31 250.32 250.33 250.4

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Variation in Labor Induction

Murthy et al.

959

Appendix 1 (Continued) PTL

CH

Thyroid disease

UTI

Heart disease

Renal disease

Diabetes mellitus 250.40 250.41 250.42 250.43 250.5 250.50 250.51 250.52 250.53 250.6 250.60 Downloaded by: National University of Singapore. Copyrighted material.

250.61 250.62 250.63 250.7 250.70 250.71 250.72 250.73 250.8 250.80 250.81 250.82 250.83 250.9 250.90 250.91 250.92 250.93 357.2 360.2 362.0 362.01 366.41 648.0 648.00 648.01 648.02 648.03 6,483.04 Abbreviations: CH, chronic hypertension; PTL, preterm labor; UTI, urinary tract infection.

American Journal of Perinatology

Vol. 32

No. 10/2015

Hospital of Delivery and the Racial Differences in Late Preterm and Early-Term Labor Induction.

To estimate the interhospital differences in induction of labor (IOL) from 34(0/7) to 38(6/7) weeks' gestation by race/ethnicity...
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