Fertility and hormone function
A woman’s menstrual cycle is regulated by hormones which are secreted by the hypothalamus, the hypophysis or pituitary gland, and the ovaries. These hormones stimulate ovaries in order for a mature egg cell to be produced and for the uterus to prepare for a healthy pregnancy.
Beginning of cycle
The hypothalamus secretes GnRH (gonadotropin-releasing hormone) which stimulates the release of FSH (follicle stimulation hormone) and LH (Luteinizing hormone) from the pituitary gland. These two types of hormones work together: FSH creates follicles and LH induces their maturation, which results in ovulation.
Follicular phase (1st – 14th day)
Once FSH levels rise, a number of follicles develop, about 8-12, but just one becomes dominant and reaches maturation. These follicles secrete E2 hormone, the levels of which rise according to the number and size of follicles. This specific hormone induces proliferation of endometrium and widening of the cervical canal, and promotes mucus release which allows the survival and movement of sperm.
Luteal phase (15th -28th)
Luteinizing hormone surges and induces ovulation, during which an egg is released from the mature follicle (13th -14th day). After ovulation, the remaining parts of the dominant follicle transform into the corpus luteum, whose role is essential: it produces progesterone to support early pregnancy. If implantation of an embryo does not occur, the corpus luteum atrophies and dies and LH and FSH levels drop.