Progesterone is a steroid hormone that plays an important role in women's reproductive health. It is produced mainly by the corpus luteum during ovulation and later by the placenta during pregnancy. Progesterone helps prepare the uterus for implantation of a fertilized egg, thickens the lining of the uterus to prevent bleeding after childbirth, and suppresses immune responses that could reject an embryo as foreign tissue. It also plays a role in regulating menstrual cycles and maintaining pregnancy. In addition, progesterone has other functions such as reducing inflammation, improving mood, and promoting the growth of breast tissue.