First-Trimester Working Conditions and Birthweight: A Prospective Cohort Study

Objectives. We investigated the relationship between women's first-trimester working conditions and infant birthweight. Methods. Pregnant women (N=8266) participating in the Amsterdam Born Children and Their Development study completed a questionnaire gathering information on employment and working conditions. After exclusions, 7135 women remained in our analyses. Low birthweight and delivery of a small-for-gestational-age (SGA) infant were the main outcome measures. Results. After adjustment, a workweek of 32 hours or more (mean birthweight decrease of 43 g) and high job strain (mean birthweight decrease of 72 g) were significantly associated with birthweight. Only high job strain increased the risk of delivering an SGA infant (odds ratio [OR]=1.5; 95% confidence interval [CI]=1.1, 2.2). After adjustment, the combination of high job strain and a long workweek resulted in the largest birthweight reduction (150 g) and the highest risk of delivering an SGA infant (OR=2.0; 95% CI=1.2, 3.2). Conclusions. High levels of job strain during early pregnancy are associated with reduced birthweight and an increased risk of delivering an SGA infant, particularly if mothers work 32 or more hours per week. (Am J Public Health. 2009;99:1409-1416. doi:10.2105/AJPH.2008.138412