Alteration in vaginal microflora, douching prior to pregnancy, and preterm birth.

We aimed to determine the relationship of douching prior to pregnancy and bacterial vaginosis (BV) during pregnancy on preterm birth, addressing individual and joint effects. We used a prospective cohort study and assessed vaginal microflora using gram stains and Nugent's criteria. Douching behaviour was based on self-report about the 12 months prior to pregnancy. Preterm births were categorised as spontaneous or medically indicated. A total of 2561 women provided vaginal specimens and 1492 provided self-reports on douching behaviour. Bacterial vaginosis assessed at 24-28 weeks' gestation in the absence of douching prior to pregnancy was associated with spontaneous preterm birth (odds ratio = 2.74 [95% confidence interval 1.13, 6.66]) as was douching in the absence of BV (OR = 2.20 [1.29, 3.75]). The combination of BV and douching was unrelated to spontaneous or medically indicated preterm birth. We concluded that acute alterations in vaginal microflora at mid-pregnancy or douching prior to pregnancy were associated with an increased risk of preterm birth, but the combination did not appear to increase the risk further than would be expected.

Factors that influence the timing of spontaneous labor at term.

OBJECTIVE: Whether pre-term birth culminates as a result of a de novo pathologic process or is more simply early activation of physiologic mechanisms is unknown. Exploration of the onset of labor in term women with classical risk factors for early delivery might provide insights into the mechanisms leading to pre-term birth. This study examines whether sociodemographic factors known to increase the risk of pre-term birth also affect the length of term gestations. METHODS: From a large prospective cohort composed of women delivering from 1995-2000, a sample was selected of 441 women from Central North Carolina, US, who delivered singletons after 37 weeks gestation. An algorithm was designed to identify induced labors and gestational age was censored at the time of induction. Gestational age was assigned by sonography and menstrual dating. Data were analysed using the Cox proportional hazards model. The main outcome measure was time to spontaneous labor. RESULTS: Women with 12 years of education had longer periods of gestation than women with less than 12 years of education, HR = 0.57 [0.39, 0.84]. Shorter gestational periods were found for women with pre-term premature rupture of membranes (PPROM) in a previous pregnancy, HR = 3.70 [1.60, 8.52], even after adjusting for confounders. Smoking was not associated (p > 0.1) with the timing of labor at term. CONCLUSIONS: By studying the timing of spontaneous parturition at term we identified that there is little overlap in risk factors that affect timing of delivery between spontaneous term and pre-term births.

Poverty, education, race, and pregnancy outcome.

Few studies have considered the differing impact of socioeconomic factors on pregnancy outcomes among racial subgroups. We assessed pregnancy outcome by race, education, and income (poverty index), using data from the Pregnancy, Infection, and Nutrition Study, a cohort study of preterm birth in central North Carolina, using binomial regression. Poverty was associated with an increased risk of preterm birth only among African Americans with 12 or more years of education (RR=1.6, 95% CI: 1.1, 2.2). White participants with both a low level of education and an income below the poverty line were at increased risk of preterm birth (RR=1.7, 95% CI: 1.1, 2.7). White women with 12 or more years of education had increased risk of small-for-gestational-age birth (SGA, defined as <10th percentile of birth weight for gestational age) associated with poverty status (RR=1.7, 95% CI: 1.1, 2.7). Socioeconomic indicators appear to have complex joint effect patterns among racial subgroups, perhaps because the material and psychological implications of education and income status differ between groups.

Probability samples of area births versus clinic populations for reproductive epidemiology studies.

Studies of pregnancy outcome are generally based either on geographically defined populations, often from birth records, or on clinic or hospital populations. We compared women recruited into a clinic-based study, the Pregnancy, Infection, and Nutrition (PIN) Study, with women who resided in the geographical area of the study (Alamance, Orange, and Wake Counties in North Carolina) and gave birth over the corresponding time period (1996-2000). Clinic participants were more likely to be Black, younger, have lower education, be unmarried, have a more frequent history of adverse pregnancy outcome, obtain prenatal care later, and smoke more cigarettes. Despite that profile, the proportion of clinic participants delivering preterm was somewhat lower than among area women overall (10.8% vs. 11.3%). Black/White risk ratios for preterm birth were markedly different for area (1.6) vs. clinic women (1.1), whereas other predictors were similar. Patterns may differ across groups for many reasons, including self-selection of clinics and varying clinical practices.

Should spontaneous and medically indicated preterm births be separated for studying aetiology?

An increasing proportion of preterm births result from medical interventions, and the practice of aggregating all preterm births vs. splitting into spontaneous and medically indicated preterm births is inconsistent. While mechanistic and clinical arguments can be offered for either approach, we empirically evaluated the predictiveness of a range of risk factors for preterm birth in the Pregnancy, Infection, and Nutrition Study. Most influences were shared across the two subsets - African-American ethnicity, advancing age, delivery at a university medical centre, prior preterm birth and smoking. Medically indicated preterm births appeared to be associated with intensity of medical care, higher in the university medical centre and lower for the poorest women. Body mass index was positively associated with medically indicated preterm birth and inversely with spontaneous preterm birth. Given the complexity of the aetiological pathways, both aggregation and disaggregation are well justified and should be included in studies of the causes of preterm birth.