Library · Physiology
Pregnancy: how the body changes
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During pregnancy, it is typical for several body systems to change, such as the heart and blood vessels or the urinary system, among others. They do so in response to the growing fetus, and most of those changes return to normal after delivery.
Many of them are attributed to hormones made by the placenta. The blood vessels also widen as early as the first trimester under the influence of three substances: nitric oxide, prostaglandins, and progesterone. As they widen, their resistance to blood flow, called vascular resistance, drops, and the heart responds by raising its cardiac output, meaning the amount of blood it pumps, by about 40%. If the pipes in a house get wider, the pump has to move more water to make up for it.
The blood adjusts too. Red blood cells, the cells that carry oxygen, increase by about 30%, but plasma, the liquid part of the blood, increases even more. The result is more diluted blood, like juice made with more water than concentrate. This is called physiologic anemia of pregnancy.
In brief
During pregnancy, several systems, such as the cardiovascular and urinary systems, typically change in response to the growing fetus; most return to normal after delivery.
Many changes are attributed to placental hormones. Blood vessels also dilate as early as the first trimester due to nitric oxide, prostaglandins, and progesterone; vascular resistance falls and cardiac output rises about 40% to compensate.
Red blood cells increase about 30%, but plasma increases even more: the blood becomes diluted (physiologic anemia of pregnancy).
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Maternal Changes, StatPearlsPublished
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