The American Congress of Obstetricians and Gynecologists advises pregnant women to exercise at least 30 minutes most days of the week. The organization states that regular exercise may provide relief from some of the symptoms of pregnancy and help women cope with the pains of labor. A recent study published in the June issue of the Journal of Clinical Endocrinology & Metabolism (2010; 95 [5], 2080–88) has found that physical activity during pregnancy can lead to a modest reduction in offspring birth weight.

The study included 84 first-time mothers, who were assigned to either an exercise or a control group. The exercisers participated in a maximum of five 40-minute sessions per week of moderate-intensity stationary cycling until at least the 36th week of gestation. At study completion, the researchers found that the exercise group produced babies approximately 143 ± 94 grams (about 5 ounces) lighter than those delivered by the control group. There was no effect on maternal body weight or insulin resistance. “Our findings show that regular aerobic exercise alters the maternal environment in some way that has an impact on nutrient stimulation of fetal growth, resulting in a reduction in offspring birth weight,” stated study co-author Paul Hofman, MD, from the University of Auckland in New Zealand. “Given that large birth size is associated with an increased risk of obesity, a modest reduction in birth weight may have long-term health benefits for offspring by lowering this risk later in life.”