Exercise during pregnancy: Fetal responses to current public health guidelines

OBJECTIVE: To evaluate acute fetal responses to individually prescribed exercise according to existing guidelines (U.S. Department of Health and Human Services) in active and inactive pregnant women. METHODS: Forty-five healthy pregnant women (15 nonexercisers, 15 regularly active, 15 highly active) were tested between 28 0/7 and 32 6/7 weeks of gestation. After a treadmill test to volitional fatigue, target heart rates were calculated for two subsequent 30-minute treadmill sessions: 1) moderate intensity (40-59% heart rate reserve); and 2) vigorous intensity (60-84%). All women performed the moderate test; only active women performed the vigorous test. Fetal well-being measures included umbilical artery Dopplers, fetal heart tracing and rate, and biophysical profile. Measures were obtained at rest and immediately postexercise. RESULTS: Groups were similar in age, body mass index, and gestational age. Maternal resting heart rate in the highly active group (61.6±7.2 beats per minute [bpm]) was significantly lower than the nonexercise (79.0±11.6 bpm) and regularly active (71.9±7.4 bpm) groups (P<.001). Treadmill time was longer in highly active (22.3±2.9 minutes) than regularly active (16.6±3.4) and nonexercise (12.1±3.6) groups (P<.001), reflecting higher fitness. With moderate exercise, all umbilical artery Doppler indices were similar pre-exercise and postexercise among groups. With vigorous exercise, Dopplers were similar in regularly and highly active women with statistically significant decreases postexercise (P<.05). The groupxtime interaction was not significant. Postexercise fetal heart tracings met criteria for reactivity within 20 minutes after all tests. Biophysical profile scores were reassuring. CONCLUSION: This study supports existing guidelines indicating pregnant women may begin or maintain an exercise program at moderate (inactive) or vigorous (active) intensities.