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 group × time 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.