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Cardiovascular changes during pregnancy

Your body will undergo numerous changes during pregnancy, and this is very true of your cardiovascular system, which has important implications for exercising....

The cardiovascular system is comprised of your heart, lungs, blood and veins, and is what delivers and removes oxygen (amongst other things) to your working muscles. We often refer to fitness or our amount of “puff” when we are talking about our cardiovascular system. The changes are:

• During pregnancy blood volume increases by approximately 30% and your heart rate and cardiac output are significantly elevated at rest. These changes mean that if you use heart rate limits for your aerobic training you should set your limits for training at approximately 25-30% lower than normal.

• Hematocrit levels – which describe red blood cell quantities in your blood – are lower during pregnancy, and this decreases your potential cardiac output.

• Note that your physical responses to exercise when pregnant will differ significantly and be more variable than ususal. Care must be taken to adjust your training accordingly and closely monitor your exertion levels to keep with safe limits.

• Your breathing rate will change in the first stages of pregnancy and you may experience a shortness of breath. Later in the pregnancy as the uterus presses on the diaprahgm you will find it difficult to completely fill your lungs.

• Your temperature sensitivity may change during pregnancy, and many women find themselves to be a lot warmer than before. This is due to the changes in your metabolism and your internal body temperature does increase during pregnancy. It’s a good idea to keep cool by wearing lighter clothing, exercising at cooler times of the day or indoors, and drinking plenty of water.

The above cardiovascular changes significantly reduce your upper potential for exercising, so again, pregnancy is not a time to be reaching for new personal bests! Take care to closely monitor your exertion levels at all times and listen carefully to your body. Investing in a heart rate monitor would be a wise idea (see our article on heart rate monitors), as well as becoming familiar with the PRE scale to measure exercise intensity.