Vaginal bleeding during pregnancy and preterm birth

This study investigated the relation between self-reported vaginal bleeding during pregnancy and preterm birth in a prospective cohort of 2,829 pregnant women enrolled from prenatal clinics between 1995 and 2000 in central North Carolina. The overall association between vaginal bleeding and preterm birth was modest (risk ratio (RR) = 1.3, 95% confidence interval (CI): 1.1, 1.6). Bleeding in the first trimester only was associated with earlier preterm birth (< or =34 weeks' gestation) (RR = 1.6, 95% CI: 1.1, 2.4) and preterm birth due to preterm premature rupture of the membranes (PPROM) (RR = 1.9, 95% CI: 1.1, 3.3). Bleeding in both trimesters was associated with preterm birth due to preterm labor (RR = 3.6, 95% CI: 1.9, 6.8). Bleeding of multiple episodes, on multiple days, and with more total blood loss was associated with an approximate twofold increased risk of earlier preterm birth, PPROM, and preterm labor. In contrast, bleeding in the second trimester only, of a single episode, on a single day, and with less total blood loss was not associated with any category of preterm birth. Vaginal bleeding was not associated with preterm birth among African Amercians (RR = 1.2, 95% CI: 0.9, 1.7). This study indicates that more intense but not less intense bleeding is associated with earlier preterm birth and spontaneous preterm birth presenting as PPROM or preterm labor, and it suggests that bleeding is less predictive of preterm birth among African-American compared with White women.     

Anaemia in the first but not in the second or third trimester is a risk factor for low birth weight

OBJECTIVE: To assess pregnancy outcome in women with anaemia during pregnancy. METHODS: The study design involved a retrospective chart review of all women registering for prenatal care in the area of Kuopio University Hospital between 1990 and 2000. A haemoglobin concentration below 100g/l was used as a cutoff for anaemia and affected women (N=597) were stratified by the trimester at which anaemia was diagnosed. Multiple regression analysis was used to compare obstetric outcomes in the study groups and in non-anaemic women (N=22,202). RESULTS: The frequency of anaemia was 2.6%, with 0.3% occurring in the first trimester. After controlling for confounding factors, anaemia detected in the first trimester was associated with low-birth-weight infants (OR=3.14, 95% CI: 1.35-7.28) whereas the mid- and third-trimester anaemia groups showed no significantly different outcomes when compared with the non-anaemic women. First trimester anaemia was not significantly associated with small birth weight for gestational age (OR=0.98, 95% CI: 0.41-2.17) or with premature delivery <37 weeks (OR=1.80, 95% CI: 0.72-4.49). CONCLUSIONS: Maternal anaemia detected in the first trimester is associated with low birth weight.     

Association between maternal exposure to elevated ambient sulfur dioxide during pregnancy and term low birth weight

This retrospective cohort study investigated whether the risk of delivering full term (37-44 completed weeks of gestation) low birth weight (LBW) infants is associated with differences in exposure to air pollutants in different trimesters. Full-term infants (37 completed weeks of gestation) with a birth weight below 2500 g were classified as term LBW infants. The study infants comprised 92,288 full-term live singletons identified from the Taiwan birth registry and born in the city of Taipei or Kaoshiung in Taiwan between 1995 and 1997. Maternal exposures to various air pollutants including CO, SO2, O3, NO2, and PM10 in each trimester of pregnancy was estimated as the arithmetic means of all daily measurements taken by the air quality monitoring station nearest to the district of residence of the mother at birth. The multivariable logistic regression model with adjustment for potential confounders was used to assess the independent effect of specific air pollutants on the risk of term LBW. This study suggested a 26% increase in term LBW risk given maternal ambient exposure to SO2 concentration exceeding 11.4 ppb during pregnancy compared to low exposure (<7.1 ppb) (OR=1.26, 95% CI=1.04-1.53). Since the relative risk of term LBW was reassessed according to exposure level in each trimester, mothers exposed to >12.4 ppb of SO2 in the last trimester showed 20% higher risk (OR=1.20, 95% CI=1.01-1.41) of term LBW delivery than mothers with lower exposure (<6.8 ppb). No significant elevation ORs was observed for other air pollutants.     

Vigorous leisure activity and pregnancy outcome

BACKGROUND: Preterm birth is the leading cause of perinatal mortality in North America and Europe and a major predictor of neonatal and infant morbidity. Postterm birth is associated with increased infant mortality and morbidity, as well as increased frequency of surgical or induced labor. Because vigorous leisure activity may affect timing of delivery, this study examined association between vigorous leisure activity and birth outcomes. METHODS: Women (N = 1,699) with a singleton pregnancy were recruited at 24-29 weeks' gestation from prenatal clinics in central North Carolina between 1995 and 1998. The type and duration of any regular vigorous leisure activity was assessed in a telephone interview covering the 3-month period before pregnancy and during the first and second trimesters of pregnancy. RESULTS: The prevalence of vigorous leisure activity was 22% before pregnancy, 14% during the first trimester, and 8% during the second trimester. Vigorous leisure activity before pregnancy was unrelated to preterm (<37 weeks) as compared with term delivery (37 to <42 weeks). The risk of preterm birth was somewhat reduced with vigorous leisure activity during the first trimester (odds ratio = 0.80; 95% confidence interval = 0.48-1.35) and more so during the second trimester (odds ratio = 0.52; 95% confidence interval = 0.24-1.11). Vigorous leisure activity before pregnancy or during the first or second trimester was not associated with postterm delivery (>/=42 weeks). CONCLUSIONS: Vigorous leisure activity during the first trimester, and even more so in the second trimester, was associated with a reduced risk of preterm birth. There was no association with postterm birth. To address the etiologic role of activity on pregnancy outcome and to overcome self-selection, a randomized clinical trial would be needed.     

Maternal smoking, low birth weight, and ethnicity in relation to sudden infant death syndrome

To determine independent effects of maternal smoking and infant low birth weight (less than 2,500 g) on risk of sudden infant death syndrome (SIDS) among different ethnic groups, the authors conducted a population-based case-control study based on the 1984-1989 Washington State birth record data. Two control groups were selected for 916 SIDS cases. The first one comprised 3,704 randomly selected controls, matched to cases by birth year, to describe the characteristics of the study population. In the second control group (n = 6,186), minorities were oversampled, by matching to cases on maternal race/ethnicity and birth year, to increase the power of analysis within each ethnic group. All subjects were classified into five groups on the basis of maternal race/ethnicity: white, black, American Indian, Asian, and Hispanic. After controlling for confounders, the authors found that maternal smoking was independently associated with SIDS among white (odds ratio (OR) = 2.2, 95% confidence interval (CI) 1.8-2.6), blacks (OR = 3.1, 95% CI 1.7-5.9), Asians (OR = 2.7, 95% CI 1.1-6.6, and Hispanics (OR = 5.5, 95% CI 1.4-22.0), but had little relation among American Indians (OR = 1.4, 95% Cl 0.9-2.4). Infant low birth weight was independently related to SIDS among whites (OR = 2.5, 95% Cl 1.8-3.4) and American Indians (OR = 5.5, 95% Cl 2.8-11.2) and to a lesser extent among blacks (OR = 1.9, 95% Cl 0.8-4.1), but not among Asians (OR = 1.1, 95% Cl 0.2-5.2) or Hispanics (OR = 1.2, 95% Cl 0.1-11.5). The misclassification that may occur because of the application of the same definition of low birth weight to all ethnic groups may be the main reason for the weaker association between infant low birth weight and SIDS among blacks and the absence of an association among Asians and Hispanics. Defining low birth weight as below population mean minus 1.96 standard deviations may provide better insight into the relation between low birth weight and SIDS. Understanding the reasons for the lack of a strong association between maternal smoking during pregnancy and SIDS among American Indians may enhance our knowledge of the etiology and pathogenesis of SIDS.     

Maternal, delivery, and perinatal characteristics associated with cryptorchidism: a population-based case-control study among births in Washington State

BACKGROUND: The etiology of cryptorchidism is largely unknown. To identify maternal, perinatal, and delivery characteristics associated with cryptorchidism at birth, we conducted a population-based case-control study using Washington State birth certificates linked to birth hospitalization records. METHODS: We identified 2,395 cases of cryptorchidism among male infants born in Washington State during 1986-1996, and, for comparison, we randomly selected four controls per case (N = 9,580), frequency-matched by year of birth. RESULTS: Infant characteristics associated with cryptorchidism included low birth weight (OR = 1.5; 95% CI = 1.3-1.8), small size for gestational age (OR = 1.9; 95% CI = 1.6-2.2), and breech presentation (OR = 1.7; 95% CI = 1.4-2.1). In addition to cryptorchidism, cases were more likely to have another type of congenital malformation (OR = 3.7; 95% CI = 3.2-4.2), particularly digestive (OR = 6.8; 95% CI = 3.7-12.7) or genitourinary (OR = 4.1; 95% CI = 3.0-5.6). Maternal and pregnancy characteristics associated with cryptorchidism included nulliparity (OR = 1.2; 95% CI = 1.1-1.3), maternal smoking during pregnancy (OR = 1.2; 95% CI = 1.1-1.4), and the following pregnancy complications: oligohydramnios (OR = 1.8; 95% CI = 1.3-2.6), placental abnormality (OR = 1.3; 95% CI = 1.0-1.8), and pregnancy-induced hypertension (OR = 1.6; 95% CI = 1.4-1.9). Odds ratios were similar when the analysis was restricted to term infants. CONCLUSIONS: These findings suggest that factors affecting fetal growth and development may increase the risk of cryptorchidism.     

The association of shift work and nitrous oxide exposure in pregnancy with birth weight and gestational age.

We examined the relation between shift work and occupational nitrous oxide exposure in the second trimester of pregnancy and birth weight and gestational age at delivery among the members of the Swedish Midwives Association. Eighty-four per cent of members who were registered in 1989 responded to a postal questionnaire concerning occupational exposures, including work schedule and the use of nitrous oxide, in relation to each of their pregnancies. We obtained information on births from the Swedish Medical Birth Register. We used models with allowance for dependence between births for the same woman and found that night work was associated with preterm birth (<37 weeks) [odds ratio (OR) = 5.6; 95% confidence limits (CL) = 1.9, 16.4] and to a lesser extent with low birth weight [OR = 1.9 (95% CL = 0.6, 5.8)]. Three-shift work schedule (day, evening, and night rotation) showed a possible association with preterm birth [OR = 2.3 (95% CL = 0.7, 7.3)]. Exposure to nitrous oxide use was associated with reduced birth weight (-77 gm; 95% CL = -129, -24) and an increase in the odds of infants being small for gestational age (< or = 10th percentile of weight for gestational week) (OR = 1.8; 95% CL = 1.1, 2.8).     

孕前体质指数及孕期增重对新生儿出生体重影响的前瞻性队列研究

  目的   分析孕妇孕前体质指数(body mass index, BMI)及孕期增重(gestational weight gain, GWG)与新生儿出生体重的关联性, 并探究孕妇孕前及孕中体重动态变化对新生儿低出生体重(low birth weight, LBW)及巨大儿的影响。   方法   收集中国孕产妇队列·协和纳入的孕早期孕妇孕前体重, 并随访至分娩后, 收集分娩前体重及新生儿出生结局。将孕妇孕前BMI分为低体重组、正常体重组及超重/肥胖组, 将GWG分为适宜、不足及过多组。采用多因素多分类(多项)Logistic回归分析模型探讨孕前BMI及GWG与新生儿出生体重的关系。   结果   孕前BMI及GWG与子代出生体重相关(均有P < 0.05)。孕前超重/肥胖(OR=2.339, 95% CI:1.674~2.282, P < 0.001)、GWG过多(OR=1.398, 95% CI:1.188~1.978, P=0.048)显示为巨大儿的危险因素, GWG不足(OR=1.479, 95% CI:1.461~1.679, P=0.035)显示为LBW的危险因素, GWG过多会降低LBW的发生风险(OR=0.428, 95% CI:0.225~0.817, P=0.010)。低BMI-GWG不足(OR=1.335, 95% CI:1.048~2.319, P=0.048)是LBW的危险因素; 正常BMI-GWG过多(OR=1.088, 95% CI:1.016~1.675, P=0.038)和超重/肥胖-GWG过多(OR=1.498, 95% CI:1.244~2.017, P=0.046)是巨大儿的危险因素。   结论   孕前BMI及GWG是影响新生儿出生体重的重要因素, 提示女性应合理控制孕前及孕中体重变化。     

Birth characteristics and risk of neuroblastoma in young children

The peak incidence of neuroblastoma during infancy suggests that certain prenatal or perinatal factors may be etiologically important. In this population-based study, California birth certificates were identified for 508 (86%) neuroblastoma cases diagnosed at less than 5 years of age between 1988 and 1997. For each case, two controls, matched on date of birth and gender, were randomly selected from the statewide birth registry. Results of multivariate analyses showed a reduced risk for children of Hispanic (odds ratio (OR) = 0.57, 95% confidence interval (CI): 0.43, 0.76) and "other" (OR = 0.56, 95% CI: 0.37, 0.85) race/ethnicity, compared with non-Hispanic Whites. Postterm/high birth weight delivery was associated with an increased risk of neuroblastoma compared with term/normal birth weight delivery among infants (OR = 6.99, 95% CI: 1.07, 45.55), while preterm birth appeared suggestive of a reduced risk among children 1-4 years of age. For children in this age group, the risk of neuroblastoma was elevated for cesarean delivery compared with vaginal delivery (OR = 1.72, 95% CI: 1.21, 2.47), and, for infants, the risk was reduced if the mother had had multiple previous pregnancies (OR = 0.39, 95% CI: 0.22, 0.69). These data suggest that etiologic factors associated with the prenatal and perinatal periods may be specific to age at neuroblastoma diagnosis.     

隐睾发生的危险因素研究

目的：研究隐睾发生的危险因素。方法：采用以医院为基础的1：2配比的病例对照研究方法，按统一的调查方法对99例隐睾及198例对照组面对面问卷调查。应用SAS6。12软件对所调查因素进行单因素及多因素logistic回归分析，结果：胎儿隐睾与母亲孕早期感冒伴发热（OR＝9．37，95％CI：2．25－39．09），孕期发生先兆流产（OR＝4．66，95％CI，2．02＝10．74），孕期发生先兆子痫（OR＝16．33，95％CI：1．40－191．20），父亲职业性接触农药（OR＝12．79％CI；2．90－56．43），低出生体重（OR＝5．77，95％CI：1．39－23．98），母亲怀孕年龄＜24（OR＝2．89，95％CI：1．29－4．06）呈正相关。结论：母亲孕早期感冒伴发热，孕期发生先兆流产及先兆子痫，父亲职业性接触农药，低出体重，母亲怀孕年龄＜24岁是隐睾发病的主要危险因素。     

Intergenerational and environmental factors influencing pregnancy outcomes

PURPOSE: Factors that relate to the mother's own course of growth and development might influence later reproductive performances. This study examines the effect of maternal birth weight and maternal height and maternal weight gain, on term-small for gestational age (SGA) and preterm delivery.METHODS: Data used for this study were from the South Carolina Pregnancy Risk Assessment Monitoring System (PRAMS) and birth certificate files for 1993-1995. Since PRAMS data were weighted to adjust for sampling probabilities, non-response and survey design, Survey Data Analysis (SUDAAN) software was used in all analyses.RESULTS: Maternal birth weight was strongly associated with term SGA (OR = 3.65; 95% CI = 1.83-7.29), but not preterm delivery among black mothers; it was associated with preterm delivery (OR = 1.86; 95% CI = 1.09-3.17), but not term-SGA for white mothers. Maternal birth weight was associated with term SGA among nonsmokers only (OR = 2.34; 95% CI = 1.33-4.11). Maternal weight gain modified the effect of height on birth outcomes. Among women with inadequate weight gain, there was a 3-fold increase in risk for term-SGA (OR = 3.06; 95% CI = 2.41-3.89) for short maternal height, but not for preterm delivery. Among women with adequate plus weight gain, the association between short maternal height and term-SGA was 2.7 (95% CI = 0.55-9.43) compared to 3.67 (95% CI = 0.1.41-9.56) between short maternal height and preterm delivery. Maternal weight gain also modified the effect of maternal height on both outcomes for black mothers and for nonsmokers only.CONCLUSIONS: Findings indicate the need for interventions directed to those women who can benefit most from appropriate targeted weight gain recommendations. Therefore, prevention methods should be implemented to encourage short stature women to gain adequate weight during pregnancy.     

Folic acid supplements modify the adverse effects of maternal smoking on fetal growth and neonatal complications

Maternal smoking during pregnancy leads to increased risks of neonatal complications. The use of folic acid supplements might reduce the adverse effects of smoking. We examined whether folic acid supplement use modifies the associations of maternal smoking with first trimester plasma homocysteine concentrations, fetal growth characteristics, and risks of neonatal complications. The associations were studied in 6294 mothers participating in a prospective population-based cohort study in The Netherlands. Main outcomes measurements were first trimester plasma homocysteine concentrations, fetal growth characteristics, and neonatal complications, including preterm birth, low birth weight, and small-size-for-gestational-age. Continued maternal smoking was associated with higher first trimester plasma homocysteine concentrations [difference 0.52 μmol/L (95% range = 0.20, 2.14)], lower third trimester fetal weight (difference -44 g (95% CI = -57, -31)], and birth weight [difference -148 g (95% CI = -179, -118)]. There were significant interactions between maternal smoking and folic acid supplements on all outcome measures (all P-interaction < 0.040). Among mothers who continued smoking during pregnancy, those who did not use folic acid supplements had the highest risk of delivering a child with low birth weight [OR = 3.45 (95% CI = 1.25, 9.54)] compared to those who did use periconceptional folic acid supplements. No significant effects were observed for the risks of preterm birth and small-size-for-gestational-age at birth. Our results suggest that some adverse effects of maternal smoking on fetal growth and neonatal outcomes might be reduced by the use of folic acid supplements. The observed interaction seems to be mainly driven by smoking in the first trimester only.     

Factors associated with preference for cesarean delivery

OBJECTIVE: To study factors related to preference for cesarean delivery, among pregnant women without medical complications. METHODS: A cross-sectional study was carried out among 156 pregnant women, in a private clinic in the city of Osasco, State of S?o Paulo, from October 2000 to December 2001. The pregnant women were at 28 weeks of pregnancy or more, with no formal contraindication for vaginal delivery at the time of the interview. Sociodemographic data and past and present obstetric history were assessed by applying a questionnaire. The pregnant women were specifically asked what their current preference for delivery was. Pearson's Chi-square test and logistic regression for multivariate analysis were performed with a 5% significance level. RESULTS: Sixty-seven pregnant women (42.9%) said they had little motivation to undergo vaginal delivery. In the multivariate analysis, the following variables were statistically significant: previous vaginal birth (p=0.001; ORadj=0.04; 95% CI=0.01-0.12); husband's monthly income greater than 750 reais (p=0.006, ORadj=3.44; 95% CI=1.38-8.33). The women with a previous vaginal delivery presented 25-fold lower chance of choosing cesarean delivery. The opinion that the previous delivery experience was unsatisfactory was marginally associated with the main outcome (p=0.06; ORadj=0.42; 95% CI=0.16-1.05). CONCLUSIONS: Motivation for cesarean delivery is associated with influences such as the type and degree of satisfaction with previous delivery and income.     

Effect of parents' occupational exposures on risk of stillbirth, preterm delivery, and small-for-gestational-age infants

Epidemiologic research on the effects of parental occupational exposures on fetal development has been limited. The National Natality and Fetal Mortality surveys obtained applicable data on probability samples of live births and fetal deaths which occurred in the US in 1980 among married women. Analyses were conducted for case groups of stillbirths (2,096 mothers, 3,170 fathers), preterm deliveries (less than 37 weeks completed gestation) (363 mothers, 552 fathers), and small-for-gestational-age infants (218 mothers, 371 fathers) compared with controls. Occupational exposures were defined by industry of employment and by imputed exposures based on a job-exposure linkage system. For stillbirth, maternal work in the rubber, plastics, and synthetics industry (odds ratio (OR) = 1.8, 95% confidence interval (Cl) 0.8-4.0) and lead exposure (OR = 1.6, 95% Cl 0.8-3.1), and paternal employment in the textile industry (OR = 1.9, 95% Cl 1.2-2.9), had the largest odds ratios. Preterm birth was most strongly associated with maternal lead exposure (OR = 2.3, 95% Cl 0.7-7.0), corroborating previous findings. Twofold increased risk of preterm delivery was found with paternal employment in the glass, clay, and stone; textile; and mining industries. Paternal exposures to x-rays and polyvinyl alcohol were associated with 1.5-fold increase in risk. The occupation of the mother was not associated with delivery of a small-for-gestational-age infant, in contrast to paternal employment in the art (OR = 2.6, 95% Cl 1.2-5.6) and textile industries (OR = 2.5, 95% Cl 1.3-4.7). Several toxic agents were associated with risk elevation of 1.3 or greater for fathers, most notably benzene (OR = 1.5, 95% Cl 1.1-2.3). In spite of limitations in the exposure data, the size of the exposed populations, and possible confounding, the results in this study encourage further evaluation of the effects of maternal exposure to lead and possibly solvents, as well as paternal exposure in the textile industry and to x-rays and benzene.     

The effect of vaginal bleeding during pregnancy on preterm and small-for-gestational-age births: US National Maternal and Infant Health Survey, 1988

We examined the effects of vaginal bleeding during pregnancy on preterm and small-for-gestational-age (SGA) births using data from the 1988 US National Maternal and Infant Health Survey. We examined the severity of vaginal bleeding and separated the preterm births into subsets by the degree of prematurity (< 32, 32-33, 34-36 weeks' gestation). We also evaluated associations stratified by race. Multiple logistic regression analysis showed that vaginal bleeding was associated with an increased risk of preterm birth, with a more pronounced elevated risk for preterm birth before 34 weeks' gestation and a notably stronger association for more severe bleeding that occurred in both the first and the second half of pregnancy. Odds ratios, but not risk differences, for birth before 34 weeks' gestation were greater for white women with vaginal bleeding than for black women. There was no association between vaginal bleeding during pregnancy and SGA births.     

The effect of ambient carbon monoxide on low birth weight among children born in southern California between 1989 and 1993.

We evaluated the effect of carbon monoxide (CO) exposures during the last trimester of pregnancy on the frequency of low birth weight among neonates born 1989-1993 to women living in the Los Angeles, California, area. Using birth certificate data for that period, we assembled a retrospective cohort of infants whose mothers resided within 2 miles of 1 of 18 CO monitoring stations. Based on the gestational age and birth date of each child, we estimated last-trimester exposure by averaging the corresponding 3 months of daily CO concentrations registered at the monitoring station closest to the mother's residence (determined from the birth certificate). Where data were available (at 6 stations), we also averaged measurements taken daily for nitrogen dioxide and ozone and those taken at 6-day intervals for particulate matter [less than/equal to]10 microm (PM10) to approximate last-trimester exposures to other pollutants. Overall, the study cohort consisted of 125,573 singleton children, excluding infants born before 37 or after 44 weeks of gestation, those weighing below 1,000 or above 5,500 g at birth, those for whom fewer than 10 days of CO measurements were available during the last trimester, and those whose mothers suffered from hypertension, diabetes, or uterine bleeding during pregnancy. Within the cohort, 2,813 (2.2%) were low in birth weight (between 1,000 and 2,499 g). Exposure to higher levels of ambient CO (>5.5 ppm 3-month average) during the last trimester was associated with a significantly increased risk for low birth weight [odds ratio (OR) = 1.22; 95% confidence interval (CI), 1.03-1.44] after adjustment for potential confounders, including commuting habits in the monitoring area, sex of the child, level of prenatal care, and age, ethnicity, and education of the mother.     

Residential mobility patterns and exposure misclassification in epidemiologic studies of birth defects

Many studies of environmental exposures and birth defects use mothers' addresses at delivery as a proxy for the exposure. The validity of these studies is questionable because birth defects generally occur within 8 weeks of conception and the mother's address at delivery may differ from her address early in pregnancy. In order to assess the extent of this bias, we examined the pattern of maternal residential mobility over the span of 3 months prior to conception through delivery, and associated maternal socio-demographic characteristics. We linked Texas subjects from a national case-control study of birth defects with their corresponding records from the Texas Birth Defects Registry and the Texas live birth certificates. Logistic regression analyses were conducted to assess maternal socio-demographic factors related to mobility during pregnancy. Overall, 33% of case and 31% of control mothers changed residence between conception and delivery. The pattern of mobility was similar for both case and control mothers for each pregnancy period. Multivariate analyses indicated that for case mothers, older age (OR=0.39, 95% CI=0.21-0.70), higher household income (OR=0.35, 95% CI=0.18-0.68), Hispanic ethnicity (OR=0.64, 95% CI=0.44-0.92), and higher parity (OR=0.59, 95% CI=0.38-0.94) were indicators of lower mobility during pregnancy. For control mothers, the same pattern of association was present, however, only older age was significantly associated with low rates of mobility. Studies of birth defects using maternal address at delivery as a proxy for maternal environmental exposures during pregnancy may be subject to considerable nondifferential exposure misclassification due to maternal mobility during pregnancy.     

Outdoor air pollution, low birth weight, and prematurity

This study tested the hypothesis, suggested by several recent reports, that air pollution may increase the risk of adverse birth outcomes. This study analyzed all singleton live births registered by the Czech national birth register in 1991 in 67 districts where at least one pollutant was monitored in 1990-1991 (n = 108,173). Maternal exposures to sulfur dioxide (SO(2)), total suspended particles (TSP), and nitrous oxides (NO(x)) in each trimester of pregnancy were estimated as the arithmetic means of all daily measurements taken by all monitors in the district of birth of each infant. Odds ratios of low birth weight (< 2,500 g), prematurity (< 37 weeks of gestation), and intrauterine growth retardation (IUGR; < 10th percentile of birth weight for gestational age and sex) were estimated by robust logistic regression. The median (and 25th and 75th percentile) trimester exposures were 32 (18, 56) microg/m(3) for SO(2); 72 (55, 87) microg/m(3) for TSP; and 38 (23, 59) microg/m(3) for NO(x). Low birth weight (prevalence 5.2%) and prematurity (prevalence 4.8%) were associated with SO(2) and somewhat less strongly with TSP. IUGR was not associated with any pollutant. The effects on low birth weight and prematurity were marginally stronger for exposures in the first trimester, and were not attenuated at all by adjustment for socioeconomic factors or the month of birth. Adjusted odds ratios of low birth weight were 1.20 [95% confidence interval (CI), 1.11-1.30] and 1.15 (CI, 1.07-1.24) for a 50 microg/m(3) increase in SO(2) and TSP, respectively, in the first trimester; adjusted odds ratios of prematurity were 1.27 (CI, 1.16-1.39) and 1.18 (CI, 1.05-1.31) for a 50 microg/m(3) increase in SO(2) and TSP, respectively, in the first trimester. Low gestational age accounted for the association between SO(2) and low birth weight. These findings provide further support for the hypothesis that air pollution can affect the outcome of pregnancy.     

In utero exposure to steroid contraceptives and outcome of pregnancy.

A cohort study of women who used steroid contraceptives during pregnancy was conducted in Chiang Mai, northern Thailand, between 1984 and 1987. There were 1,573 pregnancies in which the fetus was exposed to the injectable contraceptive Depo-Provera (The Upjohn Company, Kalamazoo, Michigan) (830 accidental pregnancies and 743 infants conceived before the mother started use of Depo-Provera), 601 accidental pregnancies in women who were using oral contraceptives, and 2,578 planned pregnancies with no steroid exposures (controls). Subjects were followed up for interview, and medical records were traced for birth weight. Women using Depo-Provera had more risk factors for adverse pregnancy outcomes than did the other groups. The adjusted odds ratios for low birth weight were increased for accidental pregnancies with fetal exposure to Depo-Provera (odds ratio (OR) = 1.5, 95% confidence interval (Cl) 1.2-1.9) or oral contraceptives (OR = 1.5, 95% Cl 1.2-2.0). The higher risk of low birth weight among infants exposed in utero to Depo-Provera or oral contraceptives is due in part to self-selection for adverse outcomes among women with unplanned pregnancies. However, among accidental pregnancies with Depo-Provera, the risk of low birth weight was significantly increased when conception was estimated to have occurred within 4 weeks of injection. The odds ratios were 1.9 (95% Cl 1.4-3.2) for injection-to-conception intervals of less than or equal to 4 weeks, 1.5 (95% Cl 0.9-2.3) for intervals of 5-8 weeks, and 1.2 (95% Cl 0.7-1.9) for intervals of greater than or equal to 9 weeks. This trend was highly significant. Thus, the authors conclude that early, high-dose in utero exposures to Depo-Provera may affect fetal growth.     

Plasma total cysteine,pregnancy complications,and adverse pregnancy outcomes: the Hordaland Homocysteine Study

BACKGROUND: Total homocysteine (tHcy) is associated with pregnancy complications and adverse pregnancy outcomes. The associations of plasma total cysteine (tCys) with such outcomes have not been investigated in large populations. OBJECTIVE: We investigated the association between plasma tCys and pregnancy complications, congenital malformations, and other adverse pregnancy outcomes. DESIGN: The plasma tCys concentrations of 5883 women aged 40-42 y that were measured in 1992-1993 during a cardiovascular health screening were compared with the outcomes and complications of 14492 pregnancies in the same women that were registered in the Medical Birth Registry of Norway from 1967 to 1996. RESULTS: After adjustment for parity, mother's age, tHcy, total cholesterol, body mass index, smoking, and coffee drinking, high plasma tCys concentrations (above the 95th percentile) were associated with significantly higher risks of preeclampsia [n = 342; odds ratio (OR): 1.6; 95% CI: 1.1, 2.4; P = 0.03], premature delivery (n = 774; OR: 1.8; 95% CI: 1.3, 2.5; P = 0.001), and very low birth weight (n = 175; OR: 2.0; 95% CI: 1.1, 3.9; P = 0.03) than were lower plasma tCys concentrations. tCys was not associated with the risk of placental abruption. High tCys concentrations showed a weak association with congenital malformations and stillbirths with birth weight <1500 g. The associations were independent of the tHcy concentrations. CONCLUSION: High tCys concentrations were associated with risks of preeclampsia, premature delivery, and low birth weight.