Staying in touch with your body is a key factor in becoming pregnant. Understanding your personal menstrual cycle, the hormones that affect fertility and the stages your body goes through will help you better understand the complex process of conceiving. Your cycle may vary each month making it more difficult to pinpoint your most fertile days. Lets check how your harmones drive your cycle.
How Hormones Drive Your Cycle
At the start of a menstrual cycle, estrogen levels are low.
Low estrogen levels stimulate the pituitary gland to produce Follicle Stimulating Hormone (FSH), which stimulates a number of follicles in the ovary to start to develop.
The developing follicles produce estrogen, which acts to thicken the uterine wall and is responsible for the type and quantity of cervical mucus.
High estrogen levels lead to ‘sperm friendly’ mucus and the beginning of the fertile days. Fertile mucus supports sperm survival and aids in sperm transport. In the absence of fertile mucus, sperm usually only survive for a few hours.
Sperm survival coupled with the life span of an egg combine to provide typically up to a 6 day window of fertility.
As the estrogen levels rise, the cervix opens to permit sperm to enter the uterus. Typically, only one follicle becomes dominant and the others regress.
The estrogen level peaks and stimulates the pituitary to produce a surge in Luteinizing Hormone (LH). The egg will be released from the ovary 24-36 hours after this LH surge.
The egg travels into the fallopian tube to await fertilization, and can survive for up to 24 hours after ovulation. The empty follicle forms the corpus luteum, which secretes progesterone.
Progesterone reverses the effects of estrogen, causing the cervix to close and non-sperm friendly mucus to be produced.
If the egg is successfully fertilized by a sperm, estrogen and progesterone levels remain high. The egg implants itself into the uterine wall and produces human Chorionic Gonadotrophin (hCG) to maintain the pregnancy — hCG is the hormone detected by pregnancy tests.
If the egg is not fertilized, the corpus luteum degenerates, estrogen and progesterone levels fall and the uterine wall breaks down and is shed (menstruation). The pituitary detects the falling estrogen levels and produces FSH, thus beginning a new cycle.