Which hormone plays a crucial role in maintaining pregnancy?

Progesterone is the hormone that plays a crucial role in maintaining pregnancy. It is vital for establishing and maintaining the uterine lining, which is essential for the implantation of the fertilized egg. After conception, progesterone helps to prevent uterine contractions that could lead to the rejection of the developing embryo. This hormone supports the early stages of pregnancy by promoting a favorable environment within the uterus, ensuring that nutrients and oxygen are adequately supplied to the fetus.

Progesterone levels rise throughout pregnancy, particularly during the first trimester, which is critical for sustaining the pregnancy until the placenta takes over hormone production. Its influence on the immune system also helps to prevent the mother's body from rejecting the embryo as a foreign entity.

In contrast, while prolactin is important for lactation and breastfeeding, and estrogen plays a role in many reproductive functions, neither is primarily responsible for the maintenance of pregnancy in the same way that progesterone is. Somatotropin, or growth hormone, is involved in growth and metabolism but is not directly related to the processes that sustain pregnancy. Understanding the specific roles each of these hormones plays helps clarify why progesterone is essential for maintaining a healthy pregnancy.