Progesterone and its Role in Pregnancy

Progesterone is a hormone produced by the ovaries and later, if pregnancy occurs, by the placenta. Progesterone is essential to achieve and maintain a healthy pregnancy. In the second half of the menstrual cycle after ovulation, progesterone prepares the uterine lining (endometrium) to receive the fertilized egg (embryo). If implantation is successful and pregnancy occurs, progesterone continues to support the uterine lining providing the ideal environment for the growing embryo. Pregnancy is dependent on the ovary for progesterone production for the first 10 weeks of pregnancy after which time the placenta is fully capable of making enough progesterone for pregnancy support. If pregnancy does not occur, then progesterone levels fall bringing on menstrual bleeding.

Progesterone is prescribed following in vitro fertilization (IVF) because of the belief that the cells that make progesterone are damaged or removed at the time of egg retrieval. Each fertility center has its own favorite method of giving progesterone that appears to offer them their highest chance of pregnancy success. Formulations of progesterone given either vaginally, intramuscularly, or sequentially are the most common methods of application. Progesterone containing pills or in skin patches are not effective. The timing of when to stop taking progesterone once prescribed also varies depending on the individual fertility center with most centers advising discontinuing progesterone when the placenta is capable of sustaining the pregnancy on its own (10 weeks of gestation).

Progesterone may also be prescribed in women with reproductive difficulty who are attempting pregnancy but who are not having IVF especially in cases where ovulation dysfunction exists, in women over age 40, and in women with a history of recurrent pregnancy loss. In these cases progesterone administration is almost always given by vaginal inserts or suppositories.

Side effects of progesterone include tiredness, breast tenderness, and progesterone may also delay the onset of menstruation. That is why most centers recommend pregnancy testing at the time menstruation is normally expected or approximately 12 days following embryo transfer in cases of IVF.