Pregnancy is an opportune time to discuss healthy lifestyle behaviors because women are often more receptive to behaviors that can provide the optimal environment for the growing fetus. Physical activity (PA) is one healthy behavior for which benefits have been shown to outweigh the risks, even during pregnancy. Current U.S. guidelines for PA during pregnancy focus on aerobic activity, even though resistance training is the third most commonly reported activity among pregnant women. Resistance training can be implemented as a form of PA to improve muscular strength and endurance during pregnancy; however, due to unknown potential risks, physicians are generally hesitant to recommend it. Although there are many benefits of resistance training, only a few investigators have examined its effect during pregnancy directly. Therefore, the overall purpose of this study was to determine the associations between resistance training and adverse pregnancy and birth outcomes.To accomplish this, a retrospective, cross-sectional study design involving a convenience national sample of women was used to assess various forms of exercise, emphasizing resistance training. Women (n = 222) were recruited from a national health club chain via posters and completed a one-time online survey. Specifically, the Physical Activity Survey (PAS) included questions regarding ten domains of exercise, activities of daily living (ADL), and pregnancy and birth outcomes including gestational diabetes mellitus (GDM), preeclampsia/gestational hypertension, birth weight, preterm labor, gestational age at delivery, mode of delivery, and length of infant.Using multiple logistic and linear regression and Fisher exact tests, we tested the associations between weekly total physical activity (TPA) and exercise status and adverse pregnancy and birth outcomes. On average, 29% of participants engaged in resistance training 2.68 days/week for 28 minutes/session throughout gestation with a goal of improving their muscular endurance (i.e., low weight and high repetitions). Overall, the prevalence of GDM was 8.6%, preeclampsia/gestational hypertension were 11.3%, and preterm labor was 9.5%. 85.5% of participants delivered between 37-40 weeks gestation, and 65.3% had a vaginal delivery. Mean birth weights and infant lengths were 3.47 ± 0.54 kg and 51.3 ± 3.5 cm, respectively. After adjusting for prepregnancy body mass index (BMI), neither weekly TPA nor exercise status were significantly associated with any pregnancy or birth outcome. Although the logistic regression models did not achieve statistical significance, point estimates were lowest for adverse outcomes among participants who performed resistance training + aerobic exercise. There was a significant reduction in risk for preeclampsia/gestational hypertension (p = 0.03), while there was marginal significance for GDM (p = 0.06) and preterm labor (p = 0.07) by exercise status. No association was found between exercise status and birth weight (0.60), infant length (0.07), mode of delivery (p = 0.39), and gestational age at delivery (0.33). In general, prepregnancy BMI influenced the outcome more than weekly TPA or exercise status.In summary, our results suggest that exercising women who perform resistance training for muscular endurance, approximately three days/week for thirty minutes, do not significantly increase their risk for an adverse outcome during pregnancy.
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