David A. Savitz

Epidemiologic characteristics of preterm delivery: etiologic heterogeneity.

Preterm delivery (less than 37 weeks completed gestation) is known to result from diverse etiologic pathways, which can be grouped into idiopathic preterm labor, preterm premature rupture of the membranes, and medical complications. Data from publications providing sufficient detail to subdivide preterm delivery cases into these groups were tabulated. In spite of inconsistent terminology and incomplete reporting, patterns were identified. Black women have a markedly higher risk of preterm delivery, which is especially pronounced for preterm premature rupture of the membranes. Idiopathic preterm labor is predominant in lower-risk, white populations. These observations encourage consideration of subcategories of preterm delivery in studies of etiology and prevention.

Epidemiologic evidence on the health effects of perfluorooctanoic acid (PFOA).

Objective and sources We reviewed the epidemiologic literature for PFOA. Data synthesis Perfluorooctanoic acid (PFOA) does not occur naturally but is present in the serum of most residents of industrialized countries (U.S. median, 4 ng/mL). Drinking water is the primary route of exposure in some populations, but exposure sources are not well understood. PFOA has been used to manufacture such products as Gore-Tex and Teflon. PFOA does not break down in the environment; the human half-life is estimated at about 3 years. PFOA is not metabolized in the body; it is not lipophilic. PFOA is not directly genotoxic; animal data indicate that it can cause several types of tumors and neonatal death and may have toxic effects on the immune, liver, and endocrine systems. Data on the human health effects of PFOA are sparse. There is relatively consistent evidence of modest positive associations with cholesterol and uric acid, although the magnitude of the cholesterol effect is inconsistent across different exposure levels. There is some but much less consistent evidence of a modest positive correlation with liver enzymes. Most findings come from cross-sectional studies, limiting conclusions. Two occupational cohort studies do not provide consistent evidence for chronic disease; both are limited by sample size and reliance on mortality data. Reproductive data have increased recently but are inconsistent, and any observed adverse effects are modest. Conclusions Epidemiologic evidence remains limited, and to date data are insufficient to draw firm conclusions regarding the role of PFOA for any of the diseases of concern.

Epidemiology of health effects of radiofrequency exposure.

We have undertaken a comprehensive review of epidemiologic studies about the effects of radiofrequency fields (RFs) on human health in order to summarize the current state of knowledge, explain the methodologic issues that are involved, and aid in the planning of future studies. There have been a large number of occupational studies over several decades, particularly on cancer, cardiovascular disease, adverse reproductive outcome, and cataract, in relation to RF exposure. More recently, there have been studies of residential exposure, mainly from radio and television transmitters, and especially focusing on leukemia. There have also been studies of mobile telephone users, particularly on brain tumors and less often on other cancers and on symptoms. Results of these studies to date give no consistent or convincing evidence of a causal relation between RF exposure and any adverse health effect. On the other hand, the studies have too many deficiencies to rule out an association. A key concern across all studies is the quality of assessment of RF exposure. Despite the ubiquity of new technologies using RFs, little is known about population exposure from RF sources and even less about the relative importance of different sources. Other cautions are that mobile phone studies to date have been able to address only relatively short lag periods, that almost no data are available on the consequences of childhood exposure, and that published data largely concentrate on a small number of outcomes, especially brain tumor and leukemia.

Maternal Prepregnancy Overweight and Obesity and the Pattern of Labor Progression in Term Nulliparous Women

OBJECTIVE: To examine the effect of maternal overweight and obesity on labor progression. METHODS: We analyzed data from 612 nulliparous women with a term pregnancy that participated in the Pregnancy, Infection, and Nutrition Study from 1995 to 2002. The median duration of labor by each centimeter of cervical dilation was computed for normal-weight (body mass index [BMI] 19.8–26.0 kg/m2), overweight (BMI 26.1–29.0 kg/m2), and obese (BMI > 29.0 kg/m2) women and used as a measurement of labor progression. RESULTS: After adjusting for maternal height, labor induction, membrane rupture, oxytocin use, epidural analgesia, net maternal weight gain, and fetal size, the median duration of labor from 4 to 10 cm was significantly longer for both overweight and obese women, compared with normal-weight women (7.5, 7.9, and 6.2 hours, respectively). For overweight women, the prolongation was concentrated around 4–6 cm, whereas for obese women, their labor was significantly slower before 7 cm. CONCLUSION: Labor progression in overweight and obese women was significantly slower than that of normal-weight women before 6 cm of cervical dilation. Given that nearly one half of women of childbearing age are either overweight or obese, it is critical to consider differences in labor progression by maternal prepregnancy BMI before additional interventions are performed.

Parental psychiatric disorders associated with autism spectrum disorders in the offspring.

OBJECTIVE. Autism is a developmental disorder defined by impaired social interaction, communication, and behavior. Causes and correlates of autism are largely unknown, but elevated frequencies of psychiatric disorders and distinct personality traits have been reported among the family members of individuals with autism. Linkage of data from Swedish registries was used to investigate whether hospitalization for psychiatric conditions was higher among parents of children with autism compared with control subjects. METHODS. Data sources included the Swedish Medical Birth Register (childs birth), the Swedish Multi-Generation Register (linking parents to children), and Swedish Hospital Discharge Register (hospitalization records). Children born between 1977 and 2003 who had a hospitalization record indicating autism before 10 years of age (n = 1227) were matched with 30 693 control subjects from the Swedish Medical Birth Register by gender, year of birth, and hospital. Parent diagnoses were based on an inpatient hospital diagnostic evaluation and included schizophrenia, other nonaffective psychoses, affective disorders, neurotic and personality disorders and other nonpsychotic disorders, alcohol and drug addiction and abuse, and autism. Odds ratios and 95% confidence intervals were estimated by using conditional logistic regression, adjusted for childs age, gender, hospital of birth, parents’ age, country of birth and socioeconomic status, and diagnosis of a mental disorder in the other parent. RESULTS. Parents of children with autism were more likely to have been hospitalized for a mental disorder than parents of control subjects. Schizophrenia was more common among case mothers and fathers compared with respective control parents. Depression and personality disorders were more common among case mothers but not fathers. CONCLUSIONS. This large population study supports the potential for familial aggregation of psychiatric conditions that may provide leads for future investigations of heritable forms of autism.

Psychosocial Factors and Preterm Birth Among African American and White Women in Central North Carolina

Objectives. We assessed associations between psychosocial factors and preterm birth, stratified by race in a prospective cohort study.Methods. We surveyed 1898 women who used university and public health prenatal clinics regarding various psychosocial factors.Results. African Americans were at higher risk of preterm birth if they used distancing from problems as a coping mechanism or reported racial discrimination. Whites were at higher risk if they had high counts of negative life events or were not living with a partner. The association of pregnancy-related anxiety with preterm birth weakened when medical comorbidities were taken into account. No association with preterm birth was found for depression, general social support, or church attendance.Conclusions. Some associations between psychosocial variables and preterm birth differed by race.

Risk factors for preterm birth subtypes.

To assess epidemiologic risk factors for preterm birth subcategories in an urban population, we undertook a study of 31,107 singleton livebirths that took place at Mount Sinai Hospital in New York City between 1986 and 1994. We subdivided the preterm births into preterm premature rupture of the membranes, preterm labor, and medically induced births. We obtained information regarding the preterm subtypes and their epidemiologic risk factors from a computerized perinatal database. Adjusted odds ratios showed an increased risk for all three preterm birth subtypes in women who were black (1.9 for preterm premature rupture of membranes, 2.1 for preterm labor, and 1.7 for medically induced births) or Hispanic (1.7 for preterm premature rupture of membranes, 1.9 for preterm labor, and 1.6 for medically induced births), those who had had a previous preterm birth (3.2 for preterm premature rupture of membranes, 4.5 for preterm labor, and 3.3 for medically induced births), those who began prenatal care after the first trimester (1.4 for preterm premature rupture of membranes, 1.3 for preterm labor, and 1.3 for medically induced births), women who had been exposed to diethylstilbestrol in utero (3.1 for preterm premature rupture of membranes, 4.1 for preterm labor, and 3.7 for medically induced births), patients with preexisting diabetes mellitus (2.2 for preterm premature rupture of membranes, 2.4 for preterm labor, and 9.5 for medically induced births), and those with antepartum bleeding (2.8 for preterm premature rupture of membranes, 3.6 for preterm labor, and 3.7 for medically induced births). Other sociodemographic, constitutional, life-style, and obstetrical characteristics differed across the groups. Variation in some of the risk factors among the preterm subtypes implies that epidemiologic assessment of the more specific outcomes would be advisable. (Epidemiology 1998;9:279–285)

Exposure to trihalomethanes and adverse pregnancy outcomes

Exposure during pregnancy to disinfection by-products in drinking water has been hypothesized to lead to several adverse reproductive outcomes. We performed a retrospective cohort study to examine the relation of trihalomethane exposure during the third trimester of pregnancy to low birthweight, term low birthweight, and preterm delivery. We matched Colorado birth certificates from January 1, 1990, through December 31, 1993, to historical water sample data with respect to time and location of maternal residence based on census block groups. After excluding births from all census block groups with no trihalomethane sample data and restricting to singleton white births with 28–42 weeks of completed gestation (>400 gm), we studied 1,893 livebirths within 28 census lock groups. We found a weak association of trihalomethane exposure during the third trimester with low birthweight (odds ratio = 2.1 for the highest exposure level; 95%confidence interval = 1.0–4.8); a large increase in risk for term low birthweight at the highest level of exposure (odds ratio = 5.9; 95% confidence interval = 2.0–17.0); and no association between exposure and preterm delivery (odds ratio = 1.0 for the highest exposure level; 95% confidence interval = 0.3–2.8). The small number of adverse outcomes reduced the precision of risk estimates, but these data indicate a potentially important relation between third trimester exposure to trihalomethanes and retarded fetal growth. (Epidemiology 1998;9: 484–489)

Home pesticide use and childhood cancer: a case-control study.

The association between childhood cancer and home pesticide use was examined in a case-control study of children under 15 years of age. Parents of 252 children diagnosed with cancer in the Denver area between 1976 and 1983 and of 222 control subjects were interviewed regarding use of home pest extermination, yard treatment, and pest strips. The strongest associations were found for yard treatments and soft tissue sarcomas (odds ratios [ORs] around 4.0) and for use of pest strips and leukemias (ORs between 1.7 and 3.0). These results suggest that use of home pesticides may be associated with some types of childhood cancer.

Pracental abruption and its association with hypertension and prolonged rupture of membranes: A methodologic review and meta-analysis*

Objective To conduct a meta-analysis of published studies on placental abruption to examine its incidence, recurrence, and association with hypertensive disorders (chronic hyper-tension and preeclampsia) and prolonged rupture of membranes (PROM) in pregnancy. Data Sources We reviewed studies on placental abruption published since 1950, based on a comprehensive literature search using MEDLINE, and by identifying studies cited in the references of published reports. Methods of Study Selection We identified 54 studies, excluding case reports on placental abruption and studies relating to placenta previa and vaginal bleeding of unknown origin. We also restricted the search to articles published in English. Tabulation, Integration, and Results Studies chosen for the meta-analysis were categorized based on their study design (case-control or cohort), where they were conducted (United States or other countries), source of the data (vital records versus other sources), and magnitude of risk (risk of abruption greater or less than 1.0%). We used both fixed- and random-effects analysis to identify sources of heterogeneity in results among studies. There were striking differences in the incidence of placental abruption between cohort (0.69%) and case-control (0.35%) studies. United States-based studies found a somewhat higher incidence both for cohort (0.81%) and case-control (0.37%) studies compared with studies conducted outside the U.S. (0.60% and 0.26%, respectively). Abruption was more than ten times more common in pregnancies preceded by a pregnancy with abruption. Chronically hypertensive patients were more than three times as likely to develop placental abruption (odds ratio [OR] 3.13, 95% confidence interval [CI] 2.04–4.80) as normotensive patients. The OR for placental abruption was 1.73 (95% CI 1.47–2.04) for patients with preeclampsia. Similarly, women with pregnancies complicated by PROM were more than three times as likely to develop placental abruption (OR 3.05, 95% CI 2.16–4.32). United States-based studies, case-control studies, and studies with an incidence of abruption greater than 1% demonstrated stronger associations between abruption and hypertension and PROM. Conclusion Risk of abruption is strongly associated with chronic hypertension, PROM, and especially abruption in a prior pregnancy, and somewhat more modestly with pre-eclampsia. The criteria for the diagnosis of placental abruption, hypertensive disorders, and PROM may have introduced variability among the results of these studies. More standardized definitions of these pregnancy complications would improve the comparability of the study results.