During exercise, your target heart rate is a percentage of your maximum heart rate. If your heart beats too fast, you can weaken your heart muscle or trigger a heart attack. While most target heart rates are calculated by age, this rate can lower when you are expecting a baby. Exercise is an important part of keeping healthy during pregnancy, but you must exercise carefully to prevent your body from overheating. Always speak to your physician about the proper heart rate zone while pregnant, as it may vary based on your individual health and fitness level.
Why Heart Rate Matters
When you exercise, your heart has to work harder to pump more oxygen-carrying blood to your muscles and tissues. This makes your heart rate, or the amount of times your heart beats per minute, increase. When you are pregnant, a high heart rate can affect your body’s ability to pump blood to your baby. Additionally, exercise that raises your heart rate too much also can raise your body’s temperature. Increased body temperature is associated with a higher risk for birth defects, particularly in your first trimester, according to Jeanne-Marie Guise, MD, an OB/GYN interviewed on BabyCenter. For this reason, you may wish to monitor your heart rate during exercise.
Target Heart Rate
Traditionally, your target heart rate is calculated by subtracting your age from 220, according to the Centers for Disease Control and Prevention. This is your maximum heart rate. Your target heart rate should be between 50 and 70 percent of your maximum heart rate. However, when you are pregnant and generally considered healthy, you should not exceed 140 beats per minute while exercising, according to Dr. Guise. Using this as a general rule may help to keep your body temperature down and heart rate at a healthy enough level.
Measuring Your Heart Rate
To ensure your heart rate remains in the target zone, you can measure your heart rate at regular intervals during exercise or wear a heart rate monitor. To manually take your heart rate, place your middle and index fingers on your wrist, just below your thumb. This is known as your radial pulse. Start counting when you feel the first heartbeat and count for either 60 seconds or 30 seconds and multiply the number by two. You also can wear a heart rate monitor on your wrist or stomach to ensure your heart rate does not go too high.
Pre-Pregnancy Exceptions
The American College of Sports Medicine recommends pregnant women exercise only to their pre-pregnancy exercise levels. This means pregnancy should not be a time when you aim to start exercising intensely. If you typically exercise at a very high intensity, talk to your physician about the right heart rate for you. Fit expectant moms may be able to exercise very hard because their hearts are more accustomed to pumping blood through their bodies. For example, very fit women ages 20 to 29 may be able to achieve a higher heart rate of 145 to 160 while exercising, according to “FitPregnancy” magazine. Those older than that may be able to exercise at a heart rate of 140 to 156 if you regularly engaged in intense and vigorous exercise prior to pregnancy.
