Which hormone is primarily involved in maintaining pregnancy?

Progesterone plays a crucial role in maintaining pregnancy by preparing the endometrium (the lining of the uterus) for the implantation of a fertilized egg. After fertilization, progesterone levels rise significantly to help sustain the pregnancy. It inhibits muscle contractions in the uterus, which could potentially lead to the rejection of the developing embryo. Additionally, progesterone supports the early stages of pregnancy by preventing ovulation and menstruation during this time. Its primary function ensures that the environment within the uterus remains conducive for the growing fetus, allowing for proper development until the placenta takes over this role.

Other hormones mentioned have different roles: insulin is important for regulating blood glucose levels, oxytocin is involved in initiating labor and milk ejection during breastfeeding, and estrogen aids in preparing the body for pregnancy and the development of female secondary sexual characteristics. However, it's progesterone that is specifically essential for creating and maintaining a stable environment for a successful pregnancy.