Some Specific Cautions for Exercise During Pregnancy * Heart rate: The original ACOG guidelines were to keep maternal heart rate under 140 beats per minute. You can estimate your heart rate by taking a six-second count, then adding a zero to your result. With the added demands and blood flow in your body, you may find that your heart rate increases far more quickly than before exercise. Some lenience is generally given to women who were highly active prior to pregnancy, but ask your doctor for their specific guidelines relative to you. Current guidelines suggest exercising at 50-60% of your Maximum Heart Rate.