Why Do Older Women Have a Harder Time Getting Pregnant?

While men create sperm throughout their adult lives, women are born with a finite number of eggs, approximately 1-2 million. In the average girl, all but 400,000 of those eggs will have disappeared by puberty, and throughout adult life approximately 1,000 eggs are lost each month.

During a womans reproductive life, only about 450 eggs ovulate; the rest having been lost. Unfortunately, what most women do not know is that this loss of eggs varies from woman to woman; some will lose eggs at a much faster rate than others. This has a tremendous impact on the odds at getting pregnant.

Women are most fertile during their late teens and 20s, and for most women, getting pregnant becomes somewhat more difficult by their mid-30s, mainly because the number, and more importantly, the quality of eggs decreases as women age. Studies have shown that by age 37, eggs decrease in quality and numbers more quickly, and becoming pregnant is more difficult.

By the time women reach the age of 43 or 44 their chances of becoming pregnant are drastically reduced, about 1-2% even with the most aggressive therapy (most women older than 43 will require donor egg to achieve a pregnancy). It is also true that over time the quality of eggs that are left in the ovaries becomes compromised. This means that the risk of having a miscarriage or a baby with birth defects increases significantly after the age of 35, and especially after 40.

Ovarian age is even more important than chronological age for fertility purposes. Ovarian reserve tests can determine both the quality and number of viable eggs in the ovaries. Various factors can negatively affect a womans ovarian reserve, including smoking, drug use, ovarian surgery, autoimmune thyroid disease, and especially a family history of early menopause. The most common test for ovarian age is the FSH (follicle stimulating hormone) level, drawn on the third day of the menstrual cycle. FSH is the hormone produced in the brain that causes the ovaries to stimulate the growth of follicles, which contain eggs. The higher the FSH level, the harder your brain is working to “wake up” your ovaries. In a sense, the cycle day-3 FSH tests the health of your ovaries.

The use of the ovarian volume and number of antral follicles as markers of ovarian reserve is even better than the FSH level. This ultrasound examination, done on the third day of the cycle, measures each ovary and the number of antral follicles (small follicles in each ovary that are 2-10 millimeters in diameter).

Decreasing ovarian volume and antral follicle count (AFC) is a normal process of aging, but the ovarian volumes become smaller and AFC becomes lower before the FSH becomes high. Women with small ovaries (less than 3 cc), and fewer than five follicles per ovary, have a greater chance of failed treatment cycles. This test is especially useful when women have no immediate plans to conceive but are thinking about getting pregnant later. A compromised ovarian volume and AFC should result in a change of priorities.