The newest guidelines from the American College of Obstetricians and Gynecologists 2015 suggest a pregnant woman should use her rate of Perceived Exertion (see image below) or the Talk Test.
Checking your heart rate during pregnancy or using a heart rate monitor is considered inaccurate. In 1985, ACOG conducted a study that resulted in their recommendation of 140 beats per minute as the maximum heart rate for a pregnant woman who is exercising. In 1996, the ACOG rescinded this guideline. So RPE or the Talk Test is the best way to measure your intensity.
RPE: see image above.
Talk Test: make sure you can speak a full sentence while exercising.
Your heart rate response changes throughout pregnancy. It increases in early pregnancy, then falls gradually but continually throughout the latter trimesters.
An overall measurement assumes that all pregnant women who are working at 140 BPM are exerting the same amount of effort. A pregnant woman is not simply pumping blood through her own body, but also her unborn child’s, a circumstance that leads to a lower volume of blood circulating than when she is not pregnant and thus, a faster heart rate to compensate.
Please note that your doctor’s recommendations supersedes this advice. So if your OB recommends you stay under 140 BPM, then that is the protocol that should be followed.
FYI: If you have are a regular exerciser, you could recognize you are pregnant because your normal routine has her heart rate going higher than usual.
Takeaway: You should avoid using a heart rate monitor to determine the right heart rate for your body during pregnancy exercise. A pregnant woman’s heart rate fluctuates throughout gestation, therefore making it difficult for you to determine from a number on a monitor how hard your body is actually working.
Please see the Prenatal Exercise Do’s & Don’ts before beginning prenatal exercise.
Athletes: Recent research indicates you should use a heart rate monitor in addition to your Rate of Perceived Exertion. Athletes tend to push through comfort levels, so tracking with a monitor is suggested.