Progesterone, unlike estrogen, has no activity on determining female sexual characteristics. Progesterone activity is to prepare the uterus for possible pregnancy by growing the endometrial lining of the uterus and receiving the fertilized egg and stimulating milk production.
Progesterone is directly responsible for maintaining and sustaining the fetus in the womb, stimulating, during the first two weeks of pregnancy, the fallopian tube and endometrial glands to secrete nutrients essential for the zygote. Uterine contractions are inhibited to prevent the fetus being expelled as it blocks prostaglandin production and decreases oxytocin sensitivity.
