Effects of maternal occupation on low birth weight and preterm birth: A prospective birth cohort study in the first trimester, the Japan environment and Children's study.

Although there are some reports that maternal occupation during pregnancy decreases birth size, the results are inconsistent. Hence, we examined the association of maternal occupation during pregnancy with infant low birth weight (LBW) and preterm birth (PB). We used data from 53 932 participants of the prospective birth cohort of the Japan Environment and Children's Study. During the first trimester, information on maternal occupational major and minor groups, type of employment, and average weekly working hours was obtained using a self-administered questionnaire. Information on LBW and PB was obtained from medical records transcribed by physicians, midwives/nurses, and/or research coordinators at birth. Associations between maternal occupation and birth outcomes were examined using logistic regression models adjusted for confounding factors. In the major occupational group, the odds ratio (95% confidence interval) of LBW in administrative and managerial workers (0.52; 0.32-0.84) was lower than that in professional and engineering workers. Among administrative and managerial workers, the percentages of LBW among management government officials (4.6%), officers of companies and organizations (4.0%), and management staff of companies and organizations (7.1%) were lower than the overall average of 8.2%. Similar results were found for LBW at full-term (Term-LBW; ≥37 weeks of gestational age). However, there were no associations between the maternal major occupational groups on PB. We observed the association of maternal occupation in the first trimester on infant LBW and Term-LBW. The results suggest that medical professionals need to advise considering maternal occupation when performing pregnancy checkups.