Association of sociodemographic variables with risk for very preterm birth in twins.

OBJECTIVE: To assess the influence of maternal race, age, marital status, and education on risk for earlier and later preterm births in twin pregnancies. METHODS: We analyzed 8109 white and 1906 black liveborn twin pregnancies in the Missouri Linked Sibship files for the years 1978-1990, using contingency tables and multiple logistic regression. RESULTS: Black twin gestations had 1.61-fold (95% confidence interval [CI] 1.46, 1.76) greater risk than whites for preterm birth before 34 weeks' gestation. However, there was no race difference after 33 weeks. Among whites, teen age, unmarried status, and education fewer than 12 years were independently associated with risk for delivery before 34 weeks in multivariate analysis (odds ratios [OR] 1.28-1.51, each P < or=.001). These associations were diminished or absent for preterm births after 33 weeks' gestation. White unmarried teen mothers with fewer than 12 years of education had 1.83-fold (95% CI 1.39, 2.40) greater risk for preterm birth before 34 weeks' gestation compared with white married women more than 19 years of age with at least 12 years of education. In blacks, this difference was 1.47-fold (95% CI 1.13, 1.92). In both races, these differences were absent after 33 weeks' gestation. CONCLUSION: Traditional sociodemographic risk factors were present for twin preterm birth, but mainly before 34 weeks' gestation. This, together with previous data from Missouri Linked Sibship files, indicates that dominant pathogenic mechanisms of early preterm birth in twin gestations are likely to be different from those causing later preterm twin birth. Therefore, gestational age should be accounted for in future studies seeking to identify predictive factors or biomechanisms for twin preterm birth.

Weighing costs and benefits of adequate prenatal care for 12,023 births in Missouri's Medicaid program, 1988.

Numerous studies have shown that the receipt of adequate prenatal care is associated with improvements in pregnancy outcome, particularly a reduction in the risk of low birth weight. Since medical costs for these low birth weight infants are several times higher than for normal birth weight infants, one would expect that medical costs for newborns would be lower for babies whose mothers have had adequate prenatal care than for those with inadequate prenatal care. Explored in this paper is whether the reduction in Medicaid costs for newborn and post-partum maternal care is greater than the increase in prenatal costs for a Medicaid population. The analysis used a file of 12,023 Missouri Medicaid records linked with the corresponding 1988 birth certificates. A modified version of the Kessner index was used to define the adequacy of prenatal care. Prenatal care costs were $233 higher for pregnancies with adequate prenatal care than for those in which prenatal care was inadequate. Newborn and post-partum costs starting within 60 days after the birth were $347 lower for the adequate prenatal care pregnancies, resulting in a savings of $1.49 for each extra $1 spent on prenatal care. Among the other factors studied in determining this benefit to cost ratio were global billing, Supplemental Food Program for Women, Infants, and Children (WIC), and participation in Medicaid under the expanded eligibility provisions that were effective in Missouri in 1988.

Prenatal participation in WIC related to Medicaid costs for Missouri newborns: 1982 update.

This study replicates a 1980 evaluation of WIC prenatal participation in Missouri by using a file of 9,086 Missouri Medicaid records matched with the corresponding birth records. This file was divided into a WIC group containing 3,261 records and a non-WIC group of 5,825 records. The 1982 results generally confirm the 1980 results, with the 1982 findings showing slightly improved pregnancy outcomes for WIC participants and slightly reduced benefit-to-cost ratios compared with the 1980 findings. In 1982, WIC participation was found to be associated with an increase in mean birth weight of 31 grams and reductions in low birth weight rates (statistically significant) and in neonatal death rates (not statistically significant). The reduction in each rate was 23 percent. WIC participation was also associated with a reduction in Medicaid costs for newborns reported within 45 days of birth amounting to $76 per participant. For every dollar spent on WIC, about 49 cents in Medicaid costs were apparently saved. However, wide 95 percent confidence intervals ($.07, $.90) make it difficult to determine precisely what impact WIC has on Federal and State budget outlays.

Differentiating the barriers to adequate prenatal care in Missouri, 1987-88.

Inadequate prenatal care has previously been identified as a significant risk factor for women who have low birth weight infants and infants who die during the neonatal period. Postpartum interviews with 1,484 primarily low-income women were conducted during 1987-88 in three areas of Missouri with the highest rates of inadequate prenatal care. The purpose of the study was to identify barriers to prenatal care and to determine which barriers differentiated between women receiving adequate and those receiving inadequate prenatal care. Women who received inadequate prenatal care were more likely to be black, unmarried, higher parity, and have less education than those who received adequate care. These women were also more likely to be poor, Medicaid-eligible, to have had an unwanted pregnancy, more stress and problems during pregnancy, and less social support. In the multivariate analysis, race and marital status lost their importance. The strongest predictor of inadequate prenatal care was women not knowing that they were pregnant in the first 4 months of pregnancy (adjusted odds ratio 9.28). To improve the rate of adequate prenatal care, society must address the issues of poverty and wantedness of pregnancy.

An overview of the Missouri dioxin studies.

Among the problems inherent in evaluating public health impacts around toxic waste sites are the difficulties in measuring exposure, our incomplete understanding of low-dose effects, the low frequency of disease incidence, the long latency period and silent course of disease development, the nonspecificity of clinical findings, and the probable multifactorial nature of diseases of interest. A multiphase approach for implementing epidemiologic studies in such settings was used in assessing the 2,3,7,8-tetrachlorodibenzodioxin (TCDD, or dioxin) contaminations in Missouri, where waste oil mixtures contaminated with dioxins were sprayed on various sites throughout the state for dust control in 1971. Although the toxic effects of dioxin have been studied extensively in animals and documented in cases of accidental high-level exposure in humans, very little is known of the human health effects, if any, produced by long-term exposure to relatively low levels of dioxin. In addition to medical epidemiologic studies, which were done to evaluate the types of problems present in groups of individuals with high-risk of environmental dioxin exposure, other studies to characterize dioxin levels in adipose tissue and serum are under way in a sample of potentially exposed (as well as in unexposed) Missouri residents. Research in these areas will continue to be pursued to develop a more complete understanding of the risks and appropriate public health interventions in situations of community exposure to environmental dioxins and other environmental contaminants.

An investigation of social and class differences in very-low birth weight outcomes: a continuing public health concern.

The objective of this study was to examine the relationship of nonmedical factors, including socioeconomic status, social class, education, race, and social support, to low birth weight. In a case-control study of all resident very-low-birth-weight births between December 1, 1989, and March 31, 1991, mothers completed an extensive survey related to their experience of pregnancy, including prenatal and postnatal care. Cases were defined as very-low-birth-weight (VLBW) infants and were matched to moderately-low-birth-weight and normal-birth-weight infants in race, age, and maternal residence. The hypothesis that social and class factors are more predictive of low birth weight than medical factors alone for women without chronic health problems was supported. Although the degree of the association varies depending on birth weight outcome, race even though addressed through matching--continued to play an important role in birth outcomes. A comparison of logistic model performance with and without the inclusion of social factors indicated the importance these variables play in prediction of birth outcomes. This is one of the few studies undertaken that explicitly investigates impact of patient factors on medical care.

Prevalence and implications of perinatal substance use in Missouri.

A study was conducted to determine the prevalence of perinatal substance use in Missouri. The population sample studied was selected according to a multi-stage probability-proportional-to-size sampling. The weighted prevalence for perinatal exposure to alcohol, tobacco or illicit substances was 31.9%, 10.8% for illicit substances, 21.9% for tobacco use, and 7.9% for self-reported alcohol use. In 1993, an estimated 23,925 perinatal exposures to licit and illicit substances occurred.

Smoking during pregnancy: Missouri longitudinal study.

Maternal smoking during pregnancy has been shown to be associated with reduced birthweight and increased fetal and infant mortality. This paper examines these patterns in first and second maternally-linked singleton pregnancies from 1978 to 1990 among 176,843 Missouri resident women with known smoking status in both pregnancies. Generally women were more likely to smoke in their second pregnancies (27.4%), than in their first (25.8%). This pattern was strongest among those whose first pregnancies occurred as teenagers, and for black women. The relationships of smoking during the first and second pregnancies to outcomes in the second pregnancies were examined primarily through multivariate logistic regression. The adjusted relative risk (RR) of low birthweight (< 2500 g) in the second pregnancy to not smoking in either pregnancy was 1.82 for those who smoked during the second pregnancy only, and 1.87 for those who smoked in both pregnancies. For those who smoked in the first pregnancy only, the RR was 0.97, not significantly different from 1. Adjusted smoking RRs for small-for-gestational age were larger, while adjusted RRs for fetal and neonatal mortality were smaller than the smoking RRs for low birthweight.

WIC prenatal participation and its relationship to newborn Medicaid costs in Missouri: a cost/benefit analysis.

The primary purpose of this study was to determine if WIC prenatal participation is associated with a reduction in Medicaid costs within 30 days after birth, and, if so, whether the reduction in Medicaid costs is greater than the WIC costs for these women. This evaluation of WIC was performed using 7,628 Missouri Medicaid records matched with their corresponding 1980 birth records. This file was then divided into a WIC group containing 1,883 records and a non-WIC comparison group of 5,745 records. WIC participation was found to be associated with the reduction in Medicaid newborn costs of about $100 per participant (95 per cent confidence interval $43,153); mother's Medicaid costs were not affected. For every dollar spent on WIC, about 83 in Medicaid costs within 30 days of birth were apparently saved according to the results of this study (95 per cent confidence interval $.40, $1.30). Reductions in low birthweight rates and NICU admission rates among WIC infants provided two possible reasons for the reduced Medicaid costs associated with WIC food supplementation. As WIC food costs increased, both mean birthweight and newborn Medicaid savings also increased. Because of possible inconsistencies in the data, similar studies are needed in other states.

Neonatal mortality in Missouri home births, 1978-84.

A study was conducted of 4,054 Missouri home births occurring from 1978 through 1984. Of the 3,645 births whose planning status was identified, 3,067 (84 per cent) were planned to be at home. Neonatal mortality was elevated for both planned (17 observed deaths vs 8.59 expected deaths) and unplanned home births (45 observed vs 33.19 expected) compared with physician-attended hospital births. Nearly all of the mortality excess for planned home births occurred in association with lesser trained attendants (12 observed vs 4.42 expected), while for unplanned home births the excess was entirely among infants weighing 1500 grams or more (19 observed vs 3.50 expected). For planned home births attended by physicians, certified nurse-midwives, or Missouri Midwife Association recognized midwives, there was little difference between observed and expected deaths (5 observed vs 3.92 expected). There also was little difference in deaths for unplanned home births weighing less than 1500 grams (26 observed vs 29.69 expected) compared with hospital births. The study provides evidence of the importance of having skilled attendants present at planned home births.

Factors associated with repetition of low birthweight: Missouri longitudinal study.

The tendency to repeat low birthweight (LBW < 2500 g) was studied in 182,285 linked first and second birth Missouri livebirths for 1978-90, of which 10,701 had first birth LBW. We examined the likelihood of LBW repetition by first birth birthweight, preterm delivery, and small-for-gestational-age (SGA) status by race, and the odd ratios (ORs) of repeat LBW for risk factors such as smoking, in comparison with ORs of second birth LBW among women with normal-weight first births. We found a strong tendency to repeat LBW (21%), especially following more extreme LBW first births. Adjusted ORs for repeat LBW were 10.1 for births that were preterm and SGA; 7.9 for preterm non-SGA; and 6.3 for SGA term births. Significant ORs of LBW repetition were found for smoking (1.52 and 1.85 for smoking in second pregnancy only and both pregnancies, respectively), short interpregnancy interval (1.33), and advanced maternal age (1.17), but the ORs were generally lower than those for women with normal-weight first births. Low pre-pregnancy weight was a significant risk factor for LBW repetition.

Exercise, employment, other daily activities, and adverse pregnancy outcomes.

The relations of exercise, employment, and other daily activities during pregnancy with pregnancy outcomes were examined using data from the Missouri Maternal and Infant Health Survey. Maternal surveys were available for the following singleton birth categories: 450 fetal deaths; 782 very low birth weight (VLBW, < 1,500 g); 802 moderately low birth weight (MLBW, 1,500-2,499 g); and 794 normal birth weight (NBW, > or = 2,500 g). All mothers were Missouri residents at the time of their December 1989 to March 1991 deliveries. It was found that VLBW mothers had exercised during pregnancy significantly less than NBW mothers. When compared with NBW mothers before pregnancy, VLBW mothers had been just as likely not to exercise as NBW mothers (odds ratio (OR) = 0.88, 95% confidence interval (CI) 0.69-1.12). During the first, second, and third trimesters, the odds ratios decreased to 0.70 (95% CI 0.53-0.92), 0.54 (95% CI 0.40-0.74), and 0.33 (95% CI 0.20-0.53), respectively. The VLBW mothers also were less likely to exercise during the third trimester than MLBW mothers (OR = 0.34, 95% CI 0.21-0.54) or mothers with fetal deaths (OR = 0.36, 95% CI 0.19-0.67). During the 3 months after pregnancy, none of the exercise odds ratios were statistically significant between groups. No significantly increased risks were found between employment during pregnancy or other daily activities and adverse pregnancy outcome. The study supports the recently relaxed guidelines of exercise during pregnancy.

The association of maternal smoking with age and cause of infant death.

Linked birth certificate and infant death certificate data from Missouri for 1979-1983 were used to explore the association of maternal smoking with age and cause of infant death. The data included 305,730 singleton white livebirths, of which 2,720 resulted in infant deaths. Using multiple logistic regression to control for the confounding effects of maternal age, parity, marital status, and education, the authors found that smoking was associated with both neonatal and post-neonatal mortality and with each cause of death except congenital anomalies. The adjusted odds ratio for smoking was higher for postneonatal deaths than neonatal deaths and was particularly high for two causes: respiratory disease (odds ratio = 3.4) and sudden infant death syndrome (odds ratio = 1.9). A moderate odds ratio (about 1.4) was found for causes attributed to the International Classification of Diseases, 9th Revision Perinatal Conditions Chapter. Although the associations for neonatal deaths and perinatal conditions were partially attributable to the effect of maternal smoking in lowering birth weight, virtually none of the excess respiratory mortality and sudden infant death syndrome mortality among the offspring of smokers was attributable to birth weight differences between the infants of smokers and nonsmokers. This suggests that respiratory deaths and sudden infant death syndrome deaths may be related to the effect of passive exposure of the infant to smoke after birth.

Reproductive outcomes of mothers with potential exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Animal laboratory studies have demonstrated that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) has fetotoxic and teratogenic effects at low doses. TCDD contamination of soil in nine residential areas of eastern Missouri began in 1971 when several horse arenas and dirt roads were sprayed for dust control with a mixture that contained waste oil and dioxin. The authors conducted an epidemiologic investigation to determine if adverse human reproductive outcomes are associated with exposure to soil contaminated with dioxin. The authors attempted to identify all births during the period of January 1, 1972 through December 31, 1982 that had potential exposure to dioxin, based on proximity of the maternal address to a location of known TCDD contamination. This group totaled 410 births. A matched set of 820 unexposed births was selected as a comparison group after being matched for maternal age and race, year of birth, hospital of birth, and plurality. The exposed group had increased risk ratios for infant, fetal, and perinatal death; low birth weight; and several subcategories of birth defects. None of these increased risk ratios for the exposed group were statistically significant. These results do not provide evidence that TCDD exposure has a substantial impact on the reproductive outcomes investigated. If TCDD does produce effects on reproductive health, a larger study and/or better measures of exposure may be needed to discover them.

Effects of fetal sex and race on risk of very preterm birth in twins.

OBJECTIVE: Our purpose was to determine whether the risk of twin preterm birth correlates with the number of male fetuses. STUDY DESIGN: Among 8109 white and 1884 black twin pregnancies in the Missouri Successive Pregnancy Birth/Death Data Set, 1978 through 1990, risk for preterm birth at various gestational ages was determined with 0, 1, or 2 male infants. RESULTS: Studied as individuals, white preterm twins <35 weeks' gestation demonstrated a 9.2% excess of male fetuses (P < .001). Adjusted for monozygosity, risk for preterm birth <35 weeks' gestation was 15.7% in white female-female pairs, 17.9% in unlike-sex white fetuses, and 20.2% in white male-male pairs (r = .999, P = .01). The effect was absent in black pregnancies and was unrelated to birth order, cesarean delivery, parity, twins' weight differential, year, or season. CONCLUSIONS: In white twin gestations the observed linear relationship between the number of male fetuses and the likelihood of preterm birth <35 weeks' gestation suggests a fetal mechanism for preterm birth <35 weeks' gestation linked to fetal sex. Studies of mechanisms for preterm birth must stratify by fetal sex and race.

The effects of maternal smoking on fetal and infant mortality.

Although maternal cigarette smoking has been shown to reduce the birth weight of an infant, previous findings on the relation between smoking and fetal and infant mortality have been inconsistent. This study used the largest data base ever available (360,000 birth, 2,500 fetal death, and 3,800 infant death certificates for Missouri residents during 1979-1983) to assess the impact of smoking on fetal and infant mortality. Multiple logistic regression was used to estimate the joint effects of maternal smoking, age, parity, education, marital status, and race on total mortality (infant plus fetal deaths). Compared with nonsmoking women having their first birth, women who smoked less than one pack of cigarettes per day had a 25% greater risk of mortality, and those who smoked one or more packs per day had a 56% greater risk. Among women having their second or higher birth, smokers experienced 30% greater mortality than nonsmokers, but there was no difference by amount smoked. The prevalence of smoking in this population was 30%. It was estimated that if all pregnant women stopped smoking, the number of fetal and infant deaths would be reduced by approximately 10%. The higher rate of mortality among blacks compared with whites could not be attributed to differences in smoking or the other four maternal characteristics studied. In fact, the black-white difference was greater among low-risk women (e.g., married multiparas aged 20 and over with high education) than among high-risk women (e.g., unmarried teenagers with low education).

Pregnancy wantedness and adverse pregnancy outcomes: differences by race and Medicaid status.

The relationship between pregnancy wantedness and adverse pregnancy outcomes was studied using data from 2,828 mothers who participated in the Missouri Maternal and Infant Health Survey. The wantedness of a pregnancy was measured using traditional classifications of mistimed and unwanted, as well as additional measures gauging how the woman felt about the pregnancy while she was pregnant. Fifty-eight percent of the very low birth weight infants and 59% of the moderately low birth weight infants resulted from unintended pregnancies, as did 62% of the normal-birth-weight infants. Logistic regression showed that mothers of very low birth weight infants were significantly more likely than those who had a normal-weight baby to report that they had felt unhappy about the pregnancy (odds ratio of 1.53). Very low birth weight was also associated with early denial of the pregnancy (1.54). Odds ratios associating these two unwantedness categories with low-birth-weight babies were higher among Medicaid recipients than among women not receiving Medicaid. Associations between very low birth weight and the denial variable were also significant among white women when very low birth weight outcomes were compared with normal outcomes, but there was no significant association among black women. There were no significant associations between low birth weight and the traditional unwantedness variables.

PIP: This study examines the relationship between pregnancy wantedness and adverse pregnancy outcomes among 2828 mothers who participated in the Missouri Maternal and Infant Health Survey. The survey was designed as a population-based case-control study of very low birth weight infants born to Missouri residents during December 1, 1989, and March 31, 1991. Infants of moderate and normal birth weight were the controls. Stillbirths were included, but multiple pregnancies were excluded. 36% of the sample were in-patients, 38% were Black, 62% were White, 23% were teenagers, 54% were in their 20s, 52% were married, and 52% lived in a major metropolitan area. 45% of mothers qualified for Medicaid. 779 women gave birth to a low birth weight infant, 799 gave birth to a moderately low birth weight infant, and 800 gave birth to a normal birth weight infant. 450 infants were stillbirths. Pregnancy wantedness was defined by traditional measures of mistimed and unwanted pregnancies as used in the NSFG and some newer measures, such as feelings about being pregnant. Six measures were used: unintended (mistimed and unwanted), mistimed, unwanted, unhappy about the pregnancy, unsure about the pregnancy, and denial of the pregnancy. Logistic regression analysis reveals that the odds of a pregnancy being unwanted if the baby was of low birth weight were greater for the following factors: smoking during pregnancy, maternal age, race, education, health status, pre-pregnancy weight-for-height, parity, infant mortality, and in-patient status at the survey date. The sample included 42% of mistimed pregnancies, and 15% each reported the pregnancy as unwanted, unhappy, or a denial. Birth weight outcomes did not vary by age or race. Low birth weight did not differentiate the wantedness of pregnancies using the timing-wantedness scale, but did distinguish on the happiness scale and denial measures.

Relation between very low birth weight and developmental delay among preschool children without disabilities.

The authors examined the relation between very low birth weight (VLBW: < 1,500 g) and possible developmental delay (DELAY) in the absence of frank developmental disability among young children. The prevalence of DELAY in a population-based cohort (Missouri resident births born from December 1989 through March 1991) of singleton VLBW children (n = 367) was compared with the prevalence of DELAY among both moderately low birth weight (MLBW: 1,500-2,499 g; n = 553) and normal birth weight (NBW: > or = 2,500 g; n = 555) singleton control children. DELAY was defined by nine measures of performance on the Denver Developmental Screening Test II at a median adjusted age of 15 months (range: 9-34 months). Subjects were asymptomatic for disabling conditions at developmental follow-up. Apparently well VLBW children were consistently at greater risk for both moderate and severe measures of DELAY and for DELAY across four functional areas than were either the MLBW (adjusted odds ratios: 1.4-2.7) or NBW children (adjusted odds ratios: 2.1-6.3). The greatest prevalence of DELAY tended to be among appropriate-for-gestational age VLBW children who were also the most premature. This study supports developmental follow-up of nondisabled VLBW children because of the significantly elevated risk for DELAY among apparently normal infants.

Maternal smoking during pregnancy: no association with congenital malformations in Missouri 1980-83.

Using a multisource birth defects registry developed by the Missouri Center for Health Statistics for the years 1980-83, we examined the relation between maternal smoking during pregnancy and the occurrence of congenital malformations. There were 288,067 live singleton births in this data set of which 10,223 had one or more congenital malformations. When adjusted for potential confounders the odds ratio for congenital malformations in the infants of women who smoked during pregnancy was not increased (odds ratio = 0.98, 95% confidence interval = 0.94 - 1.03). We examined the relation between smoking and groups of malformations using the International Classification of Diseases, 9th Revision, as well as analyzing for certain specific malformations within each group and found no increased risk for infants of smokers.

The influence of the wider use of surfactant therapy on neonatal mortality among blacks and whites.

BACKGROUND: Surfactant therapy reduces morbidity and mortality among premature infants with the respiratory distress syndrome (RDS). Fetal pulmonary surfactant matures more slowly in white than in black fetuses, and therefore RDS is more prevalent among whites than among blacks. We reasoned that the increased use of surfactant after its approval by the Food and Drug Administration (FDA) in 1990 might have reduced neonatal mortality more among whites than among blacks. METHODS: We merged vital-statistics information for all 1563 infants with very low birth weights (500 to 1500 g) born from 1987 through 1989 or in 1991 and 1992 to residents of St. Louis with clinical data from the four neonatal intensive care units in the St. Louis area; we then compared neonatal mortality during two periods, one before and one after the FDA's approval of surfactant for clinical use (1987 through 1989 and 1991 through 1992). RESULTS: The use of surfactant increased by a factor of 10 between 1987 through 1989 and 1991 through 1992. The neonatal mortality rate among all very-low-birth-weight infants decreased 17 percent, from 220.3 deaths per 1000 very-low-birth-weight babies born alive (in 1987 through 1989) to 183.9 per 1000 (in 1991 through 1992; P = 0.07). This decrease was due to a 41 percent reduction in the mortality rate among white newborns with very low birth weights (from 261.5 per 1000 to 155.5 per 1000; P = 0.003). In contrast, among black infants, the mortality rate for very-low-birth-weight infants did not change significantly (195.6 per 1000 and 196.8 per 1000). The relative risk of death among black newborns with very low birth weights as compared with white newborns with similar weights was 0.7 from 1987 through 1989 and 1.3 from 1991 through 1992 (P = 0.02). The differences in mortality were not explained by differences in access to surfactant therapy, by differences in mortality between black and white infants who received surfactant, or by differences in the use of antenatal corticosteroid therapy. CONCLUSIONS: After surfactant therapy for RDS became generally available, neonatal mortality improved more for white than for black infants with very low birth weights.