Brian J. McCarthy

Factors affecting the sex differential in neonatal mortality: The role of respiratory distress syndrome

We investigated factors affecting the sex differential in neonatal mortality rate using linked birth and death certificates of more than 300,000 infants born in Georgia between 1974 and 1977. The neonatal mortality rate was higher in male infants than in female infants (relative risk = 1.23, p less than 10(-8)) and was most pronounced for infants weighing between 1501 and 2500 gm (relative risk = 1.78, p less than 10(-8)). This differential persisted after adjustment was made for effects of several prenatal and labor-related factors. The male excess in neonatal mortality rate was most prominent during the first week of life and was found for several perinatal disorders. Respiratory distress syndrome-related mortality showed the largest male excess (relative risk = 1.57, p less than 10(-8)) and was most pronounced in infants weighing between 1501 and 2500 gm (relative risk = 2.78, p less than 10(-8)), in whom it accounted for roughly 60% of the excess. Since previous studies have shown that male infants have a higher incidence of respiratory distress syndrome but not a higher case-fatality rate, we suggest that slower lung maturation among male fetuses is a major contributing factor to the sex differential in neonatal mortality.

The epidemiology of neonatal death in twins

The epidemiology of twin pregnancies was studied with the use of data on 7,001 live-born twins from the Georgia neonatal surveillance network for the period 1974-1978. A cesarean section did not appreciably reduce the risk of neonatal death for a twin with a vertex presentation. The relative risk of such a neonatal death was 1.4 after adjustment was made for birth weight. A cesarean section did improve the outcome for breech and other presentations. Twins had a sixfold higher neonatal mortality rate than had singleton infants (p less than 0.001), which can be explained on the basis of distribution of birth weights. Twins had a weight-specific mortality rate equivalent to or significantly less than that for singletons after adjustment was made for birth weight. The relative risk of neonatal death for Twin 2 compared with Twin 1 was not significant. Breech presentation was more common in twins than in singletons, and for Twin 2 more than for Twin 1. As birth weight increased, the number of breech presentations decreased for Twin 2 but not for Twin 1. To reduce the high neonatal mortality rate for twins, the objective should be to reduce the incidence of low-birth-weight twins, rather than to increase the cesarean section rate for them.

International Collaborative Effort (ICE) on Birth Weight, Plurality, Perinatal, and Infant Mortality: III: A method of grouping underlying causes of infant death to aid international comparisons

Underlying causes of infant death, as coded in the ninth revision of the International Classification of Diseases, have been grouped into a system of seven functional categories plus one additional group of “other and unclassifiable” diagnoses. The groups comprise congenital anomalies, asphyxia related conditions, immaturity related conditions, infections, sudden death, deaths due to external causes, and other specific conditions. The groups were constructed by using a frequency distribution of underlying cause of death in 200 000 infant deaths in 1980–84 in the USA. When analysed according to age at death and according to birth weight, the distribution of the functional groups had patterns which corresponded to what might be expected clinically. Each functional group has common features which require intervention at a specific time for prevention and treatment. We propose that it is used as a tool in epide‐miological surveillance and to guide health authorities in priorities for disease control. International comparisons of time trends will be undertaken.

A parsimonious explanation for intersecting perinatal mortality curves: understanding the effects of race and of maternal smoking

BackgroundNeonatal mortality rates among black infants are lower than neonatal mortality rates among white infants at birth weights <3000 g, whereas white infants have a survival advantage at higher birth weights. This finding is also observed when birth weight-specific neonatal mortality rates are compared between infants of smokers and non-smokers. We provide a parsimonious explanation for this paradoxical phenomenon.MethodsWe used data on births in the United States in 1997 after excluding those with a birth weight <500 g or a gestational age <22 weeks. Birth weight- and gestational age-specific perinatal mortality rates were calculated per convention (using total live births at each birth weight/gestational age as the denominator) and also using the fetuses at risk of death at each gestational age.ResultsPerinatal mortality rates (calculated per convention) were lower among blacks than whites at lower birth weights and at preterm gestational ages, while blacks had higher mortality rates at higher birth weights and later gestational ages. With the fetuses-at-risk approach, mortality curves did not intersect; blacks had higher mortality rates at all gestational ages. Increases in birth rates and (especially) growth-restriction rates presaged gestational age-dependent increases in perinatal mortality. Similar findings were obtained in comparisons of smokers versus nonsmokers.ConclusionsFormulating perinatal risk based on the fetuses-at-risk approach solves the intersecting perinatal mortality curves paradox; blacks have higher perinatal mortality rates than whites and smokers have higher perinatal mortality rates than nonsmokers at all gestational ages and birth weights.

Short Communication. Age at Onset of Necrotizing Enterocolitis: an Epidemiologic Analysis

Summary: We studied the epidemiologic interrelationships among birth weight, gestational age, and age at onset of necrotizing enterocolitis of the newborn. As birth weight increased, the range of ages at onset and the mean age at onset both decreased. Weekly birth weight-specific attack rates for necrotizing enterocolitis declined sharply in all birth weight groups when the equivalent of 35–36 wk gestational age was reached. Our data are consistent with the hypothesis that the risk period for necrotizing enterocolitis is determined primarily by the maturity of the gastrointestinal tract of the newborn.

Patterns of prenatal care initiation in Georgia, 1980-1992.

Objective To determine whether characteristics in a womans first pregnancy were associated with the trimester in which she initiated prenatal care in her second pregnancy. Methods Data for white and black women whose first and second pregnancies resulted in singleton live births between 1980 and 1992 were obtained from Georgia birth certificates (n = 177,041). Adjusted relative risks (RRs) for early prenatal care in the second pregnancy were computed by logistic regression models that included trimester of prenatal care initiation, infant outcomes, or maternal conditions in the womans first pregnancy as the exposure and controlled for maternal age, education, childs year of birth, interval between first and second pregnancy, presence of fathers name on the birth certificate, and the interaction between prenatal care and education. Models were stratified by race. Results Women of both races who initiated prenatal care in the first trimester of their first pregnancies were more likely than those with delayed care to initiate prenatal care in the first trimester of their second pregnancies (RR = 1.25 and 1.63 for white and black women educated beyond high school, respectively). Both white and black women who delivered a baby with very low birth weight (RR = 1.06 and 1.15, respectively) or who suffered an infant death (RR = 1.09 and 1.31, respectively) in their first pregnancies were more likely than those who did not experience these events to begin prenatal care in the first trimester of their second pregnancies. Conclusion Women with some potentially preventable adverse infant outcomes tend to obtain earlier care in their next pregnancy. Unfortunately, women who delayed prenatal care in their first pregnancy frequently delay prenatal care in their next.

Identifying neonatal risk factors and predicting neonatal deaths in Georgia

A predictive model which identifies 38% of the neonatal deaths by isolating only 11% of the births was formulated. It utilized existing vital records data for 230,585 single live births which occurred in Georgia for the period 1974-1976, to describe factors recorded on the birth certificate which are determinants of neonatal mortality on a statewide basis. Maternal age, race, premature birth, spontaneous abortion or stillbirth, complications related to pregnancy, complications not related to pregnancy, and type of birth (multiple gestation) were found to be statistically significant. It is proposed that private physicians evaluate patients on the basis of this model to facilitate estimates of risk of a neonatal death. In addition, public health physicians could utilize this model to make informed decisions in regard to the management of public health programs directed at the care of pregnant women.

Birthweight Specific Perinatal Mortality in Greece

ABSTRACT. Data from the Greek Perinatal Study in April 1983 revealed an excessively high perinatal mortality rate of 21.6 per 1000 total births among singletons despite a low birthweight rate of only 4.5%. Comparison of perinatal mortality rates with Danish mortality rates in 1983, revealed the Greek rates to be three times higher than those in Denmark. When divided by time of death, the Greek stillbirth rates were two times higher and the early neonatal mortality rates were four times higher than the corresponding Danish rates. Subdivision of the Greek perinatal deaths using the Wigglesworth classification showed that the biggest group (40%) consisted of deaths associated with intrapartum asphyxia. The incidence of such deaths was 10 times higher than that found in Denmark. We conclude that in reducing the excessively high perinatal mortality rate in Greece special attention should be made to improve intrapartum and resuscitation techniques.

FACTORS ASSOCIATED WITH INADEQUATE PRENATAL CARE DURING THE SECOND PREGNANCIES AMONG AFRICAN‐AMERICAN WOMEN

A longitudinally linked data set for Georgia was used to identify characteristics, including previous prenatal care use and complications at the first birth, associated with prenatal care use in the second pregnancy among 8,224 African-American women. More than 70% of the women who were < 25 years of age at their first birth (younger women) and almost 40% of women who were > or = 25 years at their first birth received inadequate care with at least one of their first two births. Women who received inadequate care in their first pregnancy were more likely to receive inadequate care in their second pregnancy than women who received adequate care in their first pregnancy. Younger women with a history of a stillbirth, neonatal death, or vacuum extraction were less likely to receive inadequate care in their subsequent pregnancy. Although this study was not able to evaluate the content of prenatal care, it suggested that many African-American women may not receive sufficient care to prevent adverse pregnancy outcomes. Women who receive inadequate care in their first pregnancy must be targeted for interventions that help them overcome economic, situational, or attitudinal barriers to receiving adequate care in their next pregnancy.

International collaborative effort (ICE) on birthweight, plurality, and perinatal and infant mortality. I: Methods of data collection and analysis

This paper describes the collection and analysis of data by a group of international collaborators (International Collaborative Effort on Perinatal and Infant Mortality) interested in comparative studies on birthweight distributions and reproductive outcome. This is the first of a series of reports on the results of these studies. It gives an account of the countries or states involved, and the collection and characteristics of the data. The countries and states included sixteen of the United States, plus England and Wales, Denmark, Bavaria and North Rhine‐Westphalia from the Federal Republic of Germany, Israel, Japan, Norway, Scotland, and Sweden. The data comprised birth‐weight distributions in 500‐gram groups for all births and for singletons separately, for livebirths, stillbirths, first week deaths and, where available, late neonatal and infant deaths, from 1970 up to 1985.