When someone is pregnant, the body goes through many changes, and these can vary from person to person. Common experiences include morning sickness, swelling in the legs and feet, a faster heartbeat and increased fatigue. These changes are mainly due to the hormonal shifts and changes in the heart and blood vessels during pregnancy.

Why these changes happen

During pregnancy, the body adapts in remarkable ways to ensure that both parent and baby are getting enough nutrition and oxygen. Doctors monitor these changes and the baby’s growth during this 40-week journey to make sure everything is progressing smoothly.

Blood volume and function

To support the growing baby, the placenta and the pregnant parent, blood volume can expand up to 48% compared to pre-pregnancy levels. This includes increases in blood plasma and red blood cells. Hormones like estrogen and progesterone cause the blood vessels to widen (a process called vascular dilation) allowing them to hold the increased blood volume.

The heart also works harder during pregnancy, and it pumps out more blood every minute (called stroke volume). The sharpest rise in cardiac output occurs at the beginning of the first trimester. By 24 weeks, the heart can pump up to 45% more blood than before pregnancy. If a person is carrying twins, this increase can be up to 15% higher.

Heart rate and size

Heart rate—how fast the heart beats—also increases in the later stages of pregnancy. This extra workload causes the heart to grow in size, with the heart muscle cells becoming larger and stronger to pump blood more effectively.

Blood pressure changes

Early in a normal pregnancy, blood pressure starts to decrease and reaches a plateau during the second trimester. Blood pressure often starts to rise again during the third trimester and returns to pre-pregnant levels after delivery. However, studies have found that people who are overweight may have higher blood pressure during pregnancy, which may increase the risk of gestational hypertension.

Post-pregnancy changes

Little is known about the changes in the cardiovascular system changes after delivery. Most of the changes that occur during pregnancy can reverse to pre-pregnant levels shortly after delivery, but some of them might linger.

Recent research suggests that while pregnancy-related blood vessel changes might be beneficial for cardiovascular health, they also pose significant challenges for the body. Special care should be given to both parent and infant after the baby is born to make sure everyone is healthy.

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