Reproduction at a Glance

A woman is born with all of her eggs – typically between 200,000 and 500,000. Her ovaries are located on either side of her uterus, and each is the size of a walnut. About 15 to 20 eggs mature with each menstrual cycle. 

At the start of menstruation, the pituitary gland in the brain secretes a follicle stimulating hormone (FSH), which signals the ovaries to select and grow an egg for the cycle. If a woman has a 28-day cycle, eggs begin to mature around day 5 in fluid-filled sacs called follicles. As the eggs grow, the follicles enlarge and release estrogen to stop the FSH. Typically, one follicle will dominate and continue maturation until day 14, when a luteinizing hormone (LH) triggers ovulation and the follicle ruptures to release the egg (or possibly eggs) into the fallopian tube. If sexual intercourse has occurred recently, the sperm will be waiting in the fallopian tube to fertilize the egg. About three days later, the fertilized egg or embryo will travel down the fallopian tube into the uterus to implant into the endometrium or lining of the uterus.

This seemingly simple process requires all the right pieces with the right timing in order for conception to take place. Both male and female factors can hinder or prevent that conception, leading to infertility. In every 100 couples that are dealing with infertility, about 40 of the cases are linked to female-factor causes and another 40 involve male-factor issues. Keep in mind that some of these cases involve both male and female factors. The remaining 20 are considered “unexplained” infertility but still may be treated successfully with modern assisted reproduction techniques.

For example, three hormones are necessary for ovulation to occur: follicle stimulating hormone (FSH), estrogen and luteinizing hormone (LH). If a woman is deficient in any one of these hormones or if they are secreted at the wrong time, eggs will not develop. 

Other fertility road blocks can be structural abnormalities in the cervix or uterus. Fallopian tubes may be blocked or damaged due to scarring from pelvic inflammatory disease, surgery or sexually transmitted diseases. Endometriosis may have caused scarring or adhesions in the pelvis that interfere with the normal anatomy and processes necessary to achieve a pregnancy. Polycystic ovary disease may prevent the ovaries from producing a dominant egg follicle that will mature to ovulation.

Sperm play an equally important role in conception. If the percentage of sperm that are available, moving and/or shaped normally is low, fertilization may not occur. Sperm that lack the necessary receptors won’t bind to an egg. Sperm without enough propulsion won’t be able to swim up the fallopian tubes to fertilize the egg. Abnormal genetic material in sperm also may prevent fertilization.

Age plays a key role as well with the likelihood of pregnancy decreasing as people get older. 
For women, rates of success drop after age 30; for men, after age 50. In fact, one out of every four women has trouble conceiving between the ages of 35-39. The majority of fertile women get pregnant within three months after stopping contraception, so those under age 35 who haven't had success within a year need to see one of the Fertility Center's reproductive endocrinologists. Women who are 35 or older should consider fertility testing after six months without success on their own.