Objective: Our purpose was to investigate the impact of exercise and occupational activity on birth weight.
Study design: This case-control study involved singleton infants at > or = 34 weeks' gestation without congenital anomalies. Case subjects had birth weights at <15th percentile for gestational age, and 2 control subjects were selected per case subject. Data were collected by self-completed questionnaire and analyzed by means of logistic regression.
Results: Relative to those who participated in structured exercise 3 or 4 times per week during the third trimester, the odds of lower birth weight were substantially increased for those who exercised > or = 5 times per week (adjusted odds ratio, 4.61; 95% confidence interval, 1.73-12.32) and modestly increased for those at the other extreme, who engaged in structured exercise < or = 2 times per week (adjusted odds ratio, 2.64; 95% confidence interval, 1.29-5.39). Other factors of importance to birth weight were maternal height, prepregnancy body mass, pregnancy weight gain, smoking in the third trimester, and nulliparity.
Conclusions: Structured exercise frequency during late pregnancy is a determinant of birth weight.