Egg quality cannot be determined by looking at the egg, measuring its receptiveness to fertilization, or observing initial embryo division. Just because an embryo looks good in the lab, doesn't mean that it will implant.
Some of the contributing factors to embryo implantation failure are:
Diminished Ovarian Reserve
There are several blood tests to check for a woman's egg quality. The FSH (follicle stimulating hormone) test is done on cycle day 3. If you have elevated FSH levels on cycle day 3 you likely have diminished "ovarian reserve," so the ovary is producing less feedback signal to the pituitary gland, and the body responds by making more FSH in an effort to stimulate the ovary.
Women with elevated FSH levels have markedly decreased egg quality and rarely conceive with their own eggs (they do, however, become pregnant readily with donor eggs). The precise physiological reason for this is unclear. However, we do know that when eggs are obtained from women with elevated FSH levels, they appear normal, they fertilize normally, and undergo initial embryonic cleavage at a normal rate. However, they rarely divide beyond the 8 cell stage and almost never implant.
A newer test to check ovarian reserve is AMH or anti-Mullerian hormone, a hormone secreted by cells in developing egg sacs (follicles). The level of AMH in the blood is generally a good indicator of ovarian reserve.
Women have all the eggs they are ever going to have in their lives before they are born.
An AMH test gives us some insight into the remaining quantity of eggs and number of fertile years you may have, but it cannot tell us much about the quality of those eggs. AMH does not change during your menstrual cycle, so the blood sample can be taken at any time of the month — even while you are using oral contraception.
Ovarian Reserve Testing
Almost one in ten women who come in for infertility evaluation have such poor ovarian function that they are extremely unlikely to get pregnant. At the current time, this problem cannot be fixed. Therefore, assessment of a woman through ovarian reserve testing is the most important fertility test that a physician does.
Women have all the eggs they are ever going to have in their lives before they are born. By the time of birth, the ovarian reserve — the number of remaining eggs stored in the follicles — has already decreased dramatically. For the rest of her life, ongoing follicular depletion will reduce the number of eggs remaining in the ovaries. In fact, far more eggs will be lost by degeneration than are lost by ovulation.
Testing of ovarian reserve may also give you an idea of your reproductive lifespan and timing of menopause, as well as diagnose PCOS. Women who are on birth control (and therefore not really ovulating) are told to go off birth control for several months before the test.
A test to check your ovarian reserve usually involves two steps:
- vaginal ultrasound
- blood tests to measure hormone levels, which must be conducted when a woman is menstruating
Between the ultrasound and blood tests, a doctor can determine how many eggs you might be able to grow in one round with the help of hormones. While a 21-year-old woman might grow 30 to 40 eggs in one round, by age 40, that number drops to six or eight eggs. The older you get, the harder it becomes to produce eggs.
Bear in mind that having a low ovarian reserve now does not necessarily predict your pregnancy chances for the future; it simply predicts how many eggs you can grow now. Some women may have a low ovarian reserve but then conceive naturally.
Ovarian reserve testing is not the same thing as testing for ovulation. A woman can ovulate normally and have very regular menstrual cycles and still have a low probability of becoming pregnant.
Tests of ovarian reserve are only predictive of fertility when they come back abnormal. A normal test does not mean that the ovaries work well. It just means that no test has yet demonstrated that they work poorly. These tests do not find all women with poorly functioning ovaries.
Advanced Maternal Age
Even if FSH levels are normal, the age of the woman providing the eggs plays a major role in determining egg quality. Just as with women with elevated FSH levels, eggs obtained from women in their late 40's appear normal, fertilize normally, and undergo initial embryonic cleavage in a normal manner. However, such embryos almost never implant. Because of low implantation rates in women over 45 years old, normal FSH levels are not considered "reassuring."