Which progesterone? You can take Progesterone through the entire pregnancy, but its seldom useful after the 12th week. There is a preparation called 17-hydroxy-progesterone (17-ohp) that is often called 'progesterone, ' leading to confusion. 17-ohp is given in the second and even third trimesters to reduce early delivery - they're not the same drug or for the same purpose.
Up to 7 weeks. Progesterone supplementation can be stopped in most women after 7 weeks of pregnancy.