Luteal Phase Defect

immediately lowers the progesterone production and the secretory endometrium cannot support itself. Two things happen after this. The endometrial lining cannot last and begins to break down, eventually sloughing off at the beginning of the next cycle. In addition, a new crop of follicles starts growing so that there will be a new batch of follicles developing during the next menstrual cycle.

If a pregnancy does occur, the corpus luteum must be preserved at all costs. This is because the corpus luteum secretes progesterone that continues to support and endometrium that is healthy enough for a growing embryo. It is the trophoblast of the embryo that produces human chorionic gonadotropin, a hormone that is similar to luteinizing hormone, which prevents the breakdown of the corpus luteum. This keeps the corpus luteum alive, keeps the endometrium thick, and allows a healthy pregnancy to proceed. The corpus luteum in pregnancy is extremely large and remains large for up to five months—secreting necessary hormones, including progesterone, until the placenta is able to make enough estrogen and progesterone to support both itself and the endometrial lining.

If the egg cell is not fertilized, the corpus luteum is unable to support itself and eventually degenerates approximately 10 to 12 days after ovulation. At this point in time, it becomes a corpus luteum of menstruation, undergoes apoptosis, which is programmed cell death and is eventually phagocytized. The structure left over is nothing more than a scar. The egg is fertilized, corpus luteum grows and its stromal cells differentiate. If by some chance the corpus luteum is removed before the fourth month of pregnancy, the pregnancy cannot survive. The death of the corpus luteum is called luteolysis and happens every cycle that does not end in a pregnancy.

There is a feedback loop associated with the luteal phase that is worth mentioning. The corpus luteum produces hormones that ultimately suppress secretion of FSH and LH. The corpus luteum needs these hormones to maintain itself. In the absence of pregnancy, this feedback loop results in the death of the corpus luteum and falling levels of estrogen and progesterone. This is what triggers menstruation. If the egg is fertilized, the trophoblast makes hCG which supports the corpus luteum throughout the first part of pregnancy.

Luteal Phase Defect

There is a medical condition known as luteal phase defect in which the woman does not produce enough progesterone from the corpus luteum to last the entire luteal phase. End result is a shortened luteal phase and an inability of the corpus luteum is supports the embryo. There are several mechanisms believed to be behind this problem.

The first mechanism is thought to be related to abnormal follicular development. It is believed that there is not enough FSH and LH being secreted by the pituitary gland, which results in