Progesterone produced by the female reproductive system is critical to fertility. If progesterone levels do not increase after the midpoint of the menstrual cycle, this may signal ovulation failure, a common cause of infertility. Even if fertilization of the egg occurs, low levels of progesterone after ovulation can be the cause of implantation failure and pregnancy loss.
Progesterone in the Menstrual Cycle
In the menstrual cycle, the follicles within the ovary begin to enlarge in size as the egg inside the follicle grows and matures. The growing ovarian follicle produces the reproductive hormones progesterone and estrogen. After ovulation, when the mature egg leaves the follicle, the empty follicle transforms itself into a structure called the corpus luteum. The corpus luteum is an endocrine organ that produces increasing amounts of progesterone. Increasing levels of serum progesterone is one sign that ovulation has occurred.
Role of Progesterone in Pregnancy
If pregnancy occurs, the implanting embryo signals the corpus luteum to continue progesterone production until the growing placenta can produce sufficient progesterone on its own. The role of progesterone, produced first by the corpus luteum and later by the placenta, is to preserve the uterine lining, preventing uterine bleeding and loss of the pregnancy. If pregnancy does not occur, progesterone levels fall, the uterine lining fails to thrive and menstruation occurs.
Progesterone Supplementation
Low levels of progesterone production during the early days of pregnancy are a common cause of implantation failure and pregnancy loss in some infertile women. In some cases, low levels of progesterone can be supplemented by pharmaceutical progesterone. Physicians treating infertility may prescribe supplemental progesterone that can be taken orally, via vaginal suppositories or progesterone injections into the muscle. External sources of progesterone increase the levels of progesterone in the blood and reproductive organs, which supports the uterine lining and prevents pregnancy loss.
Genetic Cause for Low Progesterone Infertility
Dr. Anabelle Rodriguez and her colleagues at Johns Hopkins published research in the journal "Human Reproduction" reporting that some forms of infertility may be caused by a genetic variation in the B type 1 gene, SCARB 1, which appears to be critical for both maintaining normal progesterone levels and cholesterol regulation. A study of 274 women undergoing in vitro fertilization treatments revealed that women with a genetic variation of the normal gene had abnormally low levels of progesterone and none became pregnant.
