Researchers conducted a population-based, prospective cohort study to determine if regular exercise before and during pregnancy is associated with or prevents excessive birth weight in newborns (defined as 4170 g and 4362 g for offspring of nulliparous and multiparous women, respectively). More than 36,000 women in Norway with singleton pregnancies reported how often they engaged in various types of exercise during weeks 17 and 30 of pregnancy (as well as 3 months before pregnancy). Birth weights were obtained from a medical birth registry.

Mean newborn birth weight was 3682 g. Multiparous women were more likely than nulliparous women to be overweight, not to exercise, and to deliver infants with excessive birth weights. Overall, regular exercise ( $≥$ 3 times weekly) before pregnancy did not affect risk for excessive newborn weight. However, risk was substantially lower in nulliparous women who reported regular exercise than in those who reported no exercise during weeks 17 or 30 of pregnancy (adjusted odds ratios, 0.72 and 0.77).

Comment: The authors propose that the effect of maternal aerobic exercise on glucose tolerance might contribute to the lessening of risk for excessive birth weight in newborns. In 2002, the American College of Obstetricians and Gynecologists endorsed exercise during pregnancy (Obstet Gynecol 2002; 99:171) with the caveat that women should be evaluated for contraindications and the note that regular exercise during pregnancy could have particular health benefits for those with diabetes.

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