Recreational exercise and occupational activity during pregnancy and birthweight: A case-control study

OBJECTIVE: Our purpose was to investigate the impact of exercise and occupa tional activity on birth weight. STUDY DESIGN: This case-control study involved singleton infants at greater than or equal to 34 weeks' gestation without congenital anomalies. Case su bjects had birth weights at <15th percentile for gestational age, and 2 con trol subjects were selected per case subject. Data were collected by self-c ompleted questionnaire and analyzed by means of logistic regression. RESULTS: Relative to those who participated in structured exercise 3 or 4 t imes per week during the third trimester, the odds of lower birth weight we re substantially increased for those who exercised <greater than or equal t o>5 times per week (adjusted odds ratio, 4.61; 95% confidence interval, 1.7 3-12.32) and modestly increased for those at the other extreme, who engaged in structured exercise less than or equal to2 times per week (adjusted odd s ratio, 2.64; 95% confidence interval, 1.29-5.39). Other factors of import ance to birth weight were maternal height. prepregnancy body mass, pregnanc y weight gain, smoking in the third trimester, and nulliparity. CONCLUSIONS: Structured exercise frequency during late pregnancy is a deter minant of birth weight.