The Menstrual Cycle:
According to The American College of Obstetrics and Gynecology (ACOG): “A menstrual cycle is defined from the first day of menstrual bleeding (called day 1) of one menstrual period to the first day of menstrual bleeding of the next. An average menstrual cycle lasts 28 days.”
How it works:
The brain (specifically the hypothalamus and pituitary gland) and the ovaries “talk” to each other with signals called hormones. These hormones control the menstrual cycle. The hypothalamus in the brain releases a gonadotropin releasing hormone (GnRH), which then signals the pituitary gland to produce follicle stimulating hormone (FSH) and Luteinizing hormone (LH). FSH and LH both allow the egg to develop, mature and be released from the ovaries, as well as increasing the estrogen hormone. Estrogen is important in allowing the egg to mature. The egg is released in a process called ovulation. This brings the mature from the ovary to the fallopian tube where it can meet with sperm. Once ovulation occurs estrogen and progesterone hormones are made to thicken the lining of the uterus for implantation of an embryo which could result in a pregnancy. If an egg successfully “meets sperm” then progesterone is made until the embryo is 10 weeks. If the egg does not meet the sperm, estrogen and progesterone are no longer made, and the lining of the uterus is released, called menstruation. The low estrogen signals the hypothalamus to release GnRH… and the cycle continues.
Low levels of estrogen causes the brain to produce GnRH, which leads to the making of FSH and LH, which are important in egg development and increasing estrogen. Once an egg matures, ovulation occurs and there is an increase in estrogen and progesterone, which prepares the lining of the uterus for a fertilized egg. If there is no fertilized egg, a decrease in estrogen and menstruation occurs.
Based on our understanding of the menstrual cycle, you can now see why hormones can be a vital part of infertility treatments. The main goal of hormone treatments is to allow for egg maturation and ovulation. Mature eggs that begin the process of ovulation means an increased chance of getting pregnant.