Causes of Infertility: Female
When a couple is evaluated for infertility, almost half of the time it is found to be due to “female factors.” 24% of infertility is due to “male factors,” while 28% of infertility is unexplained even after evaluation. The causes of close to half of “female factor” infertility relate to anovulation, which means the ovaries are not releasing eggs regularly. Less common are problems with the woman’s Fallopian tubes, tumors in the uterus (fibroids or polyps), endometriosis, or other local problem in the woman’s reproductive organs.
30% of female infertility is due to problems in the Fallopian tubes, usually because of a past history of pelvic inflammatory disease or tubal surgery.
Clearly, one of the first things a couple trying to get pregnant needs to know is whether or not the woman is ovulating. Women with regular menstrual periods that are more or less a month apart are probably ovulating. Couples who are having trouble getting pregnant need to understand the process of ovulation, because many fertility treatments are aimed at making sure there are available eggs.
Ovaries make female hormones, including estrogen and progesterone, and also store and release eggs. All of the eggs in a woman’s ovaries are there at birth. Only one (or maybe 2) is supposed to be released from an ovary each month to make its way into the Fallopian tube and potentially meet up with a man’s sperm. The sequence of events is cyclical, which can be explained simply. A woman’s pituitary gland sends signals (in the form of FSH) to her ovaries to develop egg-containing follicles and make estrogen. One follicle enlarges the most. A hormone called LH signals the follicle to release an egg. LH signals the follicle to make the hormone progesterone to help the uterus get ready to hold an embryo. The egg then travels through the Fallopian tube, and if a sperm reaches the egg there and fertilizes the egg, it can start to grow and eventually attach to the wall of the uterus (called implantation). This sends signals to the brain, which in turn send signals to the ovaries and uterus to keep the conditions right for the growth of the baby.
If the egg just leaves the body without being fertilized, there is no message sent to continue growing the lining of the uterus. It is shed in a menstrual period. This is the point where female hormone levels are lowest. The low levels cause the brain to release a hormone to tell the ovaries to start making more estrogen and allow a follicle with an egg to develop, and the cycle repeats itself. Sometimes more than one egg is released, which is one way a woman can have twins. Sometimes no eggs are released.
When girls first start menstruating, there are often cycles in which no egg is released. As their systems mature, this usually stops, and most have cycles with the release of an egg.