Recreational exercise and occupational activity during pregnancy and birth weight: a case-control study.

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.