What is the Role of Progesterone in Pregnancy?

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  • Written By: Sarah Kay Moll
  • Edited By: Heather Bailey
  • Last Modified Date: 08 November 2019
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Progesterone is one of the hormones that, during a woman’s menstrual cycle, prepares the body for pregnancy. Progesterone in pregnancy helps the body adapt to pregnancy and helps the fetus develop. Levels of progesterone increase throughout a pregnancy, reaching a peak in the third trimester.

A steroid hormone, progesterone is produced naturally by the body. It is one of the hormones that regulates the menstrual cycle. It is also crucial for a healthy pregnancy and fetal development. Estrogen, another hormone involved in the menstrual cycle and pregnancy, increases the effects of progesterone. The presence of estrogen can increase the number of progesterone receptors in a cell.

Progesterone prepares the endometrium, or the lining of the uterus, for a pregnancy. In the presence of progesterone during the menstrual cycle, the endometrium becomes thick and contains lots of blood vessels. This change makes the uterus a hospitable place for a fertilized egg to implant. If no egg implants in the endometrium, the blood-rich tissue is expelled during a woman’s menstruation.

The follicle that releases an egg into the uterus, called the corpus luteum, is the main source of progesterone for the first ten weeks of a pregnancy. After the first ten weeks, the placenta takes over as the main producer of progesterone in pregnancy. If the corpus luteum fails to produce sufficient progesterone, it can lead to a miscarriage.


The level of progesterone in pregnancy varies between women, especially in the first trimester. The progesterone level increases during a healthy pregnancy, then drops again after birth. The drop in progesterone stimulates lactation, allowing a mother to breastfeed her newborn.

Many of the symptoms of pregnancy are due to hormonal changes in the levels of estrogen and progesterone. Nausea or morning sickness can be a result of normal hormonal activity. Progesterone in pregnancy, along with estrogen, can cause tender breasts during the first trimester, and actually enlarge the breasts during the second trimester.

Progesterone is also found in the central nervous system. It can act as a neurosteroid, affecting cells in the brain. It increases or decreases the excitability of a neuron by interacting with gated ion channels, the pathways that allow positively or negatively charged molecules into a cell.

Progesterone can also treat some of the negative symptoms of menopause. In post-menopausal women, progesterone may also decrease the risk of uterine cancer. Younger women who do not have normal menstrual periods may take progesterone to stimulate a normal menstrual cycle.


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Post 1

Progesterone levels in pregnancy increase but not as rapidly as HCG. Progesterone increases by miniscule levels every day until they peak. HCG increases by a lot as much as 60 percent every three days especially in the first trimester.

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