Effects Of Exercise During Pregnancy On Maternal Insulin Sensitivity And Offspring Growth

Abstract

Epidemiological studies have demonstrated a relationship between abnormal fetal growth and increased risk of childhood obesity and later adult disease. Previous studies have suggested that the maternal metabolic environment, in particular a reduction in maternal insulin sensitivity, contributes significantly to fetal growth. Regular aerobic exercise may therefore influence offspring size by regulating appropriate nutrient supply to the fetus, through an effect on maternal insulin sensitivity. PURPOSE: To determine the effects of regular exercise during pregnancy on maternal insulin sensitivity, potential hormonal regulators of fetal growth, neonatal and offspring size. METHODS: Healthy nulliparous women (30±4 yrs, BMI 25.5±4 kg/m2) were randomized to either a monitored stationary cycling program (n=47) or control (n=37) from 20 weeks gestation to term. Maternal insulin sensitivity was assessed at 19 and 35 weeks using minimal model analysis of the frequently sampled intravenous glucose tolerance test. Neonatal auxology was assessed within 48 hours of delivery and at one year. RESULTS: Offspring of exercisers had lower birth weights (Z-score control 0.24±0.8; exercise 0.19±0.9; p=0.03) and BMI at birth (Z-score control 0.40±0.9; exercise -0.01±0.04; p=0.04). The reduction in maternal insulin sensitivity with advancing gestation was not affected by exercise (p=0.45), and was unrelated to offspring birth size. However, exercise offspring had lower cord serum IGF-II (p=0.04) and a trend towards lower IGF-I (p=0.08), supporting an effect of exercise on endocrine regulation of fetal growth. Offspring size at one year remained lower in the exercise group, although not statistically significant due to reduced sample size at follow-up (BMI Z-score control -0.09±1.1; exercise -0.40±1.1; p=0.26). CONCLUSIONS: Regular exercise resulted in lower birth weights and leaner neonatal offspring with preliminary follow-up data suggesting a persistent effect at 1 year. However, exercise effects on offspring growth occurred independently of alterations in insulin sensitivity or markers of the maternal environment and unlike previous studies, maternal insulin sensitivity was not predictive of offspring birth size.