Nurses work in a unique occupational environment that can require rotating and night shifts, long hours, prolonged standing, heavy lifting, and exposure to chemicals and x-ray radiation. We examined first-trimester exposures among participants of the Nurses' Health Study II, a prospective cohort established in 1989. In 2001, detailed information on specific exposures during pregnancy was collected from participants for the most recent pregnancy since 1993. Among 6,838 live births, 576 (8%) were born preterm (< 37 weeks gestation). Log binomial regression was used to estimate the relative risk (RR) for preterm delivery. The final model included age, parity, work schedule, physical factors, and exposures to chemicals and x-rays. Working part-time ( < / = 20 hours a week) was associated with a lower risk for preterm delivery, compared to women who worked 20-40 hours a week [RR = 0.7, 95% confidence interval (CI) = 0.6-0.9]. Long working hours (41 or more per week) was not associated (RR = 1.0, 95% CI = 0.8-1.2). No association with preterm delivery was seen for working rotating shifts, night work, or heavy lifting. Standing nine or more hours per day was associated with a modest increased risk, compared with standing four to eight hours per day (RR = 1.2, 95% CI = 0.97-1.5). Exposure to sterilizing agents for five or more hours per day was associated with an increased risk compared to less than one hour per day (RR = 1.9, 05% CI = 1.0-3.3), however the results are based on few exposed cases of preterm delivery. These data suggest that physically demanding work and work schedule are not strong predictors of preterm labor, consistent with most previous studies.
American Journal of Epidemiology. Abstracts of the 2nd North American Congress of Epidemiology, June 21-24, 2006, Seattle, Washington