Luteal phase

In the absence of fertilization by sperm, the corpus luteum degenerates leading to a decrease in progesterone and estrogen, an increase in FSH and LH, and shedding of the endometrial lining (menses) to begin the menstrual cycle again.

It continues to grow during the luteal phase after ovulation and produces significant amounts of hormones, particularly progesterone, and, to a lesser extent, estrogen and inhibin.

Progesterone plays a vital role in making the endometrium receptive to implantation of the embryo and supportive of early pregnancy.

If implantation occurs, the corpus luteum will continue to produce progesterone for eight to twelve weeks, after which the placenta takes over this function.

Progesterone inhibits endometrial proliferation, and preserves uterine tissue in preparation for fertilized egg implantation.

The drop in progesterone leads to endometrial ischemia which will subsequently shed in the beginning of the next cycle at the start of menses.