Your heart changes with your Pregnancy

The following changes with the circulatory system during pregnancy happen week by week as early as the very first pregnancy week:

• increases in blood volume,
• cardiac output
• heart rate
• stroke volume
• decrease in arterial blood pressure

The increase in blood volume, as much as 45%, allows adequate blood to be transported to the uterus for proper development of the fetus.

Heart rate increases during pregnancy; there is as much as a 20% increase in heart rate during the second and third trimesters; early on there is an increase of around 7 beats per minute, later the increases reaches up to a 15 beat per minute increase.

Stroke volume increases as much as 10% by the end of the first trimester. With the increase in heart rate and stroke volume there is an increase in cardiac output, reaching as high as 30 to 50%. Cardiac output and heart rate begin to slowly increase in the sixth week and peak at the end of the second trimester.

The knowledge of the cardiovascular adaptations is especially important when dealing with body position during exercise. The supine position should be avoided after the first trimester; this position results in a relative obstruction of venous return and therefore a decrease in cardiac output. Additionally, continuous motionless standing should be avoided; motionless standing results in blood remaining in the legs, resulting in a lower blood pressure and a significant decrease in cardiac output.

These body changes during pregnancy are important to understand and keep in mind during exercise prescription design as well as daily living. A pregnant women should avoid standing for extended periods during exercise, leisure, as well as on the job.