Are physical activity and employment related to preterm birth and low birth weight?

OBJECTIVE: The purpose of this study was to review the validity of published studies that consider modifying physical activity during pregnancy to decrease preterm births and low birth weight. STUDY
DESIGN: Presented is a critical review of extant literature, both case-control studies and studies of pregnant women followed up in cohort fashion.
RESULTS: Studies both showing and not showing an association between employment and adverse outcome exist. However, no randomized trials have been reported. The most plausible associations exist for prolonged standing, long working hours, and lifting heavy objects.
CONCLUSION: Until the biologic basis of parturition is known, definitive conclusions are probably not possible. Proposals to require pregnancy leave for all employees seem premature. However, physicians must be sensitive to dilemmas faced by some employees and encourage voluntary leave for those placed in positions characterized by occupational fatigue.