Int
J
Gynaecol Obstet 16: 24-27, 1978
The Incidence, Complications and Predictors of Low Birth Weight Ernesto Moran Cacerest, Karen Robb Stewart 2 and Alfredo Goldsmith 2 lCeneral Hospital of the Instituto Salvadoreno del Seguro Social, San Salvador, El Salvador 2International Fertility Research Program, Research Triangle Park, North Carolina, USA
ABSTRACT Caceres EM, Stewart KR, Goldsmith A (General Hospital of the Instituto SalvadorerlO del Seguro Social, San Salvador, El Salvador, and International Fertility Research Program, Research Trian.l!.le Park, NC, USA). The incidence, complications and predictors of low birth weight. Int} Gynaecol Obstet 16: 24-27, 1978 A total of 3795 consecutive singleton deliveries occurring in the Social Security Hospital in San Salvador were analyzed to determine the incidence of low birth weight, the perinatal risks to the low birth weight infants and the probability of women with certain antenatal conditions delivering infants weighing less than 2500 gm. Infants who weighed less than 2500 gm accounted for 54.3% of the stillbirths, 52.6% of the neonatal deaths and 25.0% of the live births with one-minute Apgar scores of less than 7. Women with certain antenatal conditions evidenced a higher rate of low birth weight deliveries. Induced labor often resulted in infants of low birth weight. Previous premature labor and poor prenatal care were associated with the delivery of low birth weight infants. Slum residence and placenta previa were the risk factors with the highest probability of a low birth weight delivery.
INTRODUCTION In all obstetric units throughout the world, infants born too soon or too small carry the highest rates of mortality and morbidity. This common obstetric complication is usually referred to as prematurity. The term is ambiguous since it includes low birth weight infants «2500 gm) and immature infants «37 weeks' gestation) who weigh more than 2499 gm. The two conditions are better termed immaturity and low birth weight (LBW) since different risks are associated with each condition. Infants weighing less than 2500 gm are at a higher risk of death than infants at the same gestation who weigh more than In! J Gynaecol Obste! 16
2500 gm. Immature infants, even those weighing 2500 gm or more, have neonatal morbidities associated with immature physiologic systems. Both groups show higher than normal rates of long-term handicaps, especially those associated with the development of the central nervous system (5). Although these immature births and intrauterine growth retardations occur frequently, a cause can be found in less than half of the cases, and an antenatal condition or characteristic predictive of an LBW infant is present in an even smaller number of cases. In the Social Security Hospital in San Salvador, 3795 singleton deliveries were analyzed to determine the incidence of LBW, the perinatal risks to the LBW infant and the probability of women with certain antenatal conditions delivering an infant weighing less than 2500 gm.
MATERIALS AND METHODS From January 1, 1977, through July 31, 1977, data were gathered on mothers and their newborns at the time of delivery using the standard one-sheet Maternity Record form of the International Fertility Research Program. The rate of missing or unknown values was less than 1.0% for all items except hemoglobin (20.2%), antenatal condition (1.1%) and Apgar score (10.3%). Data on obstetric history and demographic characteristics are based on patient recall. Only neonatal deaths occurring before the mother's discharge from the hospital were recorded. All infants, including stillbirths weighing less than 1000 gm, are included in the calculation of mortality rates. Stepwise multiple regression analysis in which birth weight was the dependent variable and the independent variables, including maternal age, education, previous delivery before 37 weeks' gestation and hemoglobin level, revealed that these four var-
Predictors of low birth weight
iables accounted for less than 1% of the variance in birth weight. A statistical comparison was made between the rates of certain conditions and characteristics evident in mothers of LBW infants and in mothers of normal birth weight infants (2500 gm). The presence of certain conditions or characteristics in pregnant women indicated a higher level of risk of delivering an infant weighing less than 2500 gm. However, these predictive conditions were present in only a small percentage of the mothers who delivered LBW infants. Most LBW deliveries were not predictable based on any conditions examined in this study.
RESULTS The 6.2% of infants who weighed less 2500 gm accounted for 54.3% of the stillbirths, 52.6% of the neonatal deaths and 25.0% of the live births with one-minute Apgar scores of less than 7. The rate of LBW deliveries in this hospital is low compared to rates in other Latin American studies (6). This may indicate that our institution serves a low-risk population. The choice of 2500 gm as the cutoff point separating LBW from "normal" birth weight appears useful since the mortality rate rises sharply when the birth weight drops below 2500 gm. Stillbirth and neonatal death rates of 81.2 and 46.5/ 1000 deliveries, respectively, in LBW infants compare to rates of 4.5 and 2.5/1000, respectively, for normal birth weight infants. Although birth weight and gestation are related, the survival rate of infants weighing more than 2500 gm is greater than the rate for those weighing less than 2500 gm, regardless of gestational age (Table I). The shape of the mortality curve by gestation is different for the two weight groups. After 38 weeks' gestation, infants weighing less than 2500 gm have approximately the same mortality rate as infants weighing more than 2500 gm at 32 weeks' gestation. Increasing maturity does not compensate for the intrauterine growth retardation of the late, small-for-gestational-age infant. Also, the reported gestational age is of doubtful accuracy since it was based on the woman's recollection of her last menstrual period or on the physician's estimate. The greatly increased risk of stillbirth and neonatal death among the LBW infants makes it desirable to identify antenatally those women at highest risk of delivering an infant under 2500 gm. A stepwise regression analysis with birth weight as the dependent variable revealed that the effect of maternal education, age, previous prematurity, induction of labor and hemoglobin accounted for less
25
than 1% of the variance in birth weight (r = 0.009). However, for women with these or other risk factors, the probability of an LBW delivery is increased (Table II). The teenage mother is believed to be at higher risk of delivering an LBW infant than is her older counterpart. In this study, a comparison of LBW deliveries to women younger and older than 18 years of age revealed no significant difference in the LBW rates. There were not enough births to the very young adolescent less than 15 years of age to test for significance. The highest percentage (10%) of LBW infants appeared in the 35-39 age group. Parity was not a useful predictor of LBW. There was no significant difference among the LBW rates of infants born to nulliparous, multiparous and grand multiparous women in the sample.
Table I. Perinatal mortality rates by birth weight (neonatal deaths recorded prior to mother's hospital discharge).
Birth Weight (gm)
Stillbirth Rate per Number of 1000 InBirths fants
Neonatal Mortality Rate per 1000 Live Births
4500+ 4000-4499 3500-3999 3000-3499 2500-2999 2000-2499 1500-1999 1000-1499
J
Gynaecol Obstet 16: 24-27, 1978
The Incidence, Complications and Predictors of Low Birth Weight Ernesto Moran Cacerest, Karen Robb Stewart 2 and Alfredo Goldsmith 2 lCeneral Hospital of the Instituto Salvadoreno del Seguro Social, San Salvador, El Salvador 2International Fertility Research Program, Research Triangle Park, North Carolina, USA
ABSTRACT Caceres EM, Stewart KR, Goldsmith A (General Hospital of the Instituto SalvadorerlO del Seguro Social, San Salvador, El Salvador, and International Fertility Research Program, Research Trian.l!.le Park, NC, USA). The incidence, complications and predictors of low birth weight. Int} Gynaecol Obstet 16: 24-27, 1978 A total of 3795 consecutive singleton deliveries occurring in the Social Security Hospital in San Salvador were analyzed to determine the incidence of low birth weight, the perinatal risks to the low birth weight infants and the probability of women with certain antenatal conditions delivering infants weighing less than 2500 gm. Infants who weighed less than 2500 gm accounted for 54.3% of the stillbirths, 52.6% of the neonatal deaths and 25.0% of the live births with one-minute Apgar scores of less than 7. Women with certain antenatal conditions evidenced a higher rate of low birth weight deliveries. Induced labor often resulted in infants of low birth weight. Previous premature labor and poor prenatal care were associated with the delivery of low birth weight infants. Slum residence and placenta previa were the risk factors with the highest probability of a low birth weight delivery.
INTRODUCTION In all obstetric units throughout the world, infants born too soon or too small carry the highest rates of mortality and morbidity. This common obstetric complication is usually referred to as prematurity. The term is ambiguous since it includes low birth weight infants «2500 gm) and immature infants «37 weeks' gestation) who weigh more than 2499 gm. The two conditions are better termed immaturity and low birth weight (LBW) since different risks are associated with each condition. Infants weighing less than 2500 gm are at a higher risk of death than infants at the same gestation who weigh more than In! J Gynaecol Obste! 16
2500 gm. Immature infants, even those weighing 2500 gm or more, have neonatal morbidities associated with immature physiologic systems. Both groups show higher than normal rates of long-term handicaps, especially those associated with the development of the central nervous system (5). Although these immature births and intrauterine growth retardations occur frequently, a cause can be found in less than half of the cases, and an antenatal condition or characteristic predictive of an LBW infant is present in an even smaller number of cases. In the Social Security Hospital in San Salvador, 3795 singleton deliveries were analyzed to determine the incidence of LBW, the perinatal risks to the LBW infant and the probability of women with certain antenatal conditions delivering an infant weighing less than 2500 gm.
MATERIALS AND METHODS From January 1, 1977, through July 31, 1977, data were gathered on mothers and their newborns at the time of delivery using the standard one-sheet Maternity Record form of the International Fertility Research Program. The rate of missing or unknown values was less than 1.0% for all items except hemoglobin (20.2%), antenatal condition (1.1%) and Apgar score (10.3%). Data on obstetric history and demographic characteristics are based on patient recall. Only neonatal deaths occurring before the mother's discharge from the hospital were recorded. All infants, including stillbirths weighing less than 1000 gm, are included in the calculation of mortality rates. Stepwise multiple regression analysis in which birth weight was the dependent variable and the independent variables, including maternal age, education, previous delivery before 37 weeks' gestation and hemoglobin level, revealed that these four var-
Predictors of low birth weight
iables accounted for less than 1% of the variance in birth weight. A statistical comparison was made between the rates of certain conditions and characteristics evident in mothers of LBW infants and in mothers of normal birth weight infants (2500 gm). The presence of certain conditions or characteristics in pregnant women indicated a higher level of risk of delivering an infant weighing less than 2500 gm. However, these predictive conditions were present in only a small percentage of the mothers who delivered LBW infants. Most LBW deliveries were not predictable based on any conditions examined in this study.
RESULTS The 6.2% of infants who weighed less 2500 gm accounted for 54.3% of the stillbirths, 52.6% of the neonatal deaths and 25.0% of the live births with one-minute Apgar scores of less than 7. The rate of LBW deliveries in this hospital is low compared to rates in other Latin American studies (6). This may indicate that our institution serves a low-risk population. The choice of 2500 gm as the cutoff point separating LBW from "normal" birth weight appears useful since the mortality rate rises sharply when the birth weight drops below 2500 gm. Stillbirth and neonatal death rates of 81.2 and 46.5/ 1000 deliveries, respectively, in LBW infants compare to rates of 4.5 and 2.5/1000, respectively, for normal birth weight infants. Although birth weight and gestation are related, the survival rate of infants weighing more than 2500 gm is greater than the rate for those weighing less than 2500 gm, regardless of gestational age (Table I). The shape of the mortality curve by gestation is different for the two weight groups. After 38 weeks' gestation, infants weighing less than 2500 gm have approximately the same mortality rate as infants weighing more than 2500 gm at 32 weeks' gestation. Increasing maturity does not compensate for the intrauterine growth retardation of the late, small-for-gestational-age infant. Also, the reported gestational age is of doubtful accuracy since it was based on the woman's recollection of her last menstrual period or on the physician's estimate. The greatly increased risk of stillbirth and neonatal death among the LBW infants makes it desirable to identify antenatally those women at highest risk of delivering an infant under 2500 gm. A stepwise regression analysis with birth weight as the dependent variable revealed that the effect of maternal education, age, previous prematurity, induction of labor and hemoglobin accounted for less
25
than 1% of the variance in birth weight (r = 0.009). However, for women with these or other risk factors, the probability of an LBW delivery is increased (Table II). The teenage mother is believed to be at higher risk of delivering an LBW infant than is her older counterpart. In this study, a comparison of LBW deliveries to women younger and older than 18 years of age revealed no significant difference in the LBW rates. There were not enough births to the very young adolescent less than 15 years of age to test for significance. The highest percentage (10%) of LBW infants appeared in the 35-39 age group. Parity was not a useful predictor of LBW. There was no significant difference among the LBW rates of infants born to nulliparous, multiparous and grand multiparous women in the sample.
Table I. Perinatal mortality rates by birth weight (neonatal deaths recorded prior to mother's hospital discharge).
Birth Weight (gm)
Stillbirth Rate per Number of 1000 InBirths fants
Neonatal Mortality Rate per 1000 Live Births
4500+ 4000-4499 3500-3999 3000-3499 2500-2999 2000-2499 1500-1999 1000-1499
