This treatment is based on the presumption that there is deficiency of progesterone in the body. Progesterone is the hormone which helps in preservation of pregnancy. Progesterone is supposed to be a sedative for the uterus, in the absence of Progesterone the uterus will become active. After 32 weeks there is gradual withdrawal of progesterone from the body. So the Doctors also stop giving progesterone to the patient. Continued further, the patient will not deliver on the due date.