Many couples begin trying to have a child in their mid or late thirties. While we define infertility as a year of unprotected intercourse without success, we encourage women over the age of 35 to seek help after only 6 months of trying. This recommendation is based on the strong association between a woman’s age and her fertility.
The effect of age on fertility has been extensively studied, and we find the same trend in all couples, both those undergoing infertility treatment and those who are able to get pregnant naturally. In other words, all women begin to show a drop in their fertility beginning at the age of 35. While this drop begins as a gradual decline in fertility, it takes a sharp drop in the 40s. In fact, fertility in women approaches zero at the age of 45.
Part of the reason for this sharp drop has to do with the miscarriage rate as women age. In fact, the miscarriage rate begins to slowly rise at the age of 35 and then sharply rises at the age of 40. While the miscarriage rate for a young woman less than 35 is roughly 15-20%, it rises to 40% at the age of 40 and is around 60% at the age of 42. In other words, a woman who conceives at the age of 41 has a 50/50 chance of carrying her child to delivery.
If menopause does not naturally occur until the early 50s, why does fertility go to zero at the age of 45? This drop in fertility is totally due to the quality of the eggs. Women are given all their eggs when they are inside their mother’s womb. In fact, women have on average 7 million eggs when they are roughly 20 weeks old. Unfortunately, eggs undergo a process called atresia which means they are constantly dying off. When a woman is born, her number of eggs has already dropped to 1 million and the number drops to roughly 300,000 by the time she begins puberty at the age of 12.
While it has not been proven, we believe the “good” eggs that have a normal number of chromosomes are released early in a woman’s reproductive life and the “bad” eggs are released in the late 30s and 40s. This is probably why the fertility rate drops and the miscarriage rate increases. These miscarriages usually represent fetuses with an abnormal number of chromosomes (like Down’s Syndrome) that are not able to develop normally.
Success rates from in vitro fertilization as women age mirror the numbers given above. While women under the age of 35 have a roughly 50% chance of a success with a single try, women in their 40s have a 20-25% success rate. In fact, the chance of a live birth with IVF at the age of 43 is around 5% per attempt. For these reasons, most programs will not treat women over the age of 43 unless the couple is willing to use donor eggs .
There are also a number of tests that can check on the quality of a woman’s eggs. These are called tests for “ovarian reserve” and are most helpful in the woman under the age of 40. A good result (<12) does not increase a woman’s chance of conceiving; however, a bad result (12 or greater) will greatly reduce her chances of a successful live birth. The typical tests done are a cycle day 3 FSH and Estradiol and possibly a clomiphene citrate challenge test (CCCT). In the CCCT, medication is given on cycle days 5-9 and FSH levels are drawn both before and after the medication. FSH levels above 12 are considered abnormal and reduce the woman’s chance of a pregnancy to less than 5%.
What about the other reproductive organs, such as the uterus? Studies have shown that in fact the uterus does not seem to age and women who are willing to use donor eggs have excellent success rates even into their fifties. However, most donor egg programs will not recommend donor oocytes in a woman over the age of 50, primarily because of ethical issues surrounding pregnancy in the postmenopausal woman.
Finally a word about family history. Many women will go through a natural menopause around the same age as their mother. Therefore, if your mother had an early menopause, please seek a consultation with a reproductive endocrinologist, fertility specialist. While we can’t reverse the effect of age on fertility, we can recommend testing and possibly more aggressive treatment.
