Which hormone is primarily responsible for maintaining pregnancy?

Progesterone is the primary hormone responsible for maintaining pregnancy. Its role begins shortly after conception, where it helps to prepare the uterine lining for implantation. Once a fertilized embryo implants into the uterine wall, progesterone continues to play a crucial role in sustaining the pregnancy. It maintains the integrity of the uterine lining, preventing menstruation, and inhibits uterine contractions, which is essential for allowing the developing fetus to grow.

As pregnancy progresses, progesterone is produced initially by the corpus luteum and later by the placenta, supporting various functions necessary for fetal development and preparing the breasts for lactation post-delivery. This hormone creates a favorable environment for the embryo and helps modulate immune responses to protect the fetus.

While estrogen supports pregnancy as well, particularly in the development of the placenta and in stimulating uterine growth, it does not have the same direct role in maintaining the pregnancy as progesterone does. Relaxin is primarily involved in preparing the body for childbirth, and oxytocin plays a significant role during labor by stimulating contractions; however, neither is primarily responsible for maintaining the pregnancy itself.