Background: Swimmers can be exposed to high levels of trihalomethanes, byproducts of chlorination disinfection. There are no published studies on the relation between swimming and birth weight. We explored this relation in a large birth cohort, the Avon (England) Longitudinal Study of Parents and Children (ALSPAC), in 1991-1992.
Methods: Information on the amount of swimming per week during the first 18-20 weeks of pregnancy was available for 11,462 pregnant women. Fifty-nine percent never swam, 31% swam up to 1 hour per week, and 10% swam for longer. We used linear regression to explore the relation between birth weight and the amount of swimming, with adjustment for gestational age, maternal age, parity, maternal education level, ethnicity, housing tenure, drug use, smoking and alcohol consumption.
Results: We found little effect of the amount of swimming on birth weight. More highly educated women were more likely to swim compared with less educated women, whereas smokers were less likely to swim compared with nonsmokers.
Conclusions: There appears to be no relation between the duration of swimming and birth weight.