Which hormone is primarily responsible for maintaining pregnancy in females?

Progesterone is the primary hormone responsible for maintaining pregnancy in females. After fertilization, the corpus luteum in the ovaries produces progesterone, which plays a crucial role during the first trimester of pregnancy. This hormone prepares the endometrium (the lining of the uterus) to support the developing embryo by thickening it and providing a suitable environment for implantation. Additionally, progesterone helps to suppress the maternal immune response to prevent rejection of the genetically different embryo and inhibits uterine contractions, thus maintaining a stable environment for fetal development.

While estrogen also plays an important role in pregnancy, particularly in the development of the placenta and the growth of the uterus, its primary function is supportive rather than maintaining the pregnancy itself. Testosterone is primarily associated with male development and reproductive functions and does not play a critical role in maintaining pregnancy in females. Relaxin, produced by the ovaries and placenta, aids in relaxing the uterus and preparing the body for labor, but it is not the primary hormone for maintaining pregnancy.