ACOG has released a new study concluding that it is safe to start exercise at the time of pregnancy. They go even further to say that you may exercise at a moderate intensity if you are inactive, and at a vigorous intensity if you are active. Please read below for the details of their study.

Exercise During Pregnancy
Fetal Responses to Current Public Health Guidelines
Linda M. Szymanski

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 non-exercisers, 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 post-exercise.

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(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 postexer- cise 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. Postex- ercise 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.