Egg reserve means the number and quality of eggs remaining in the ovaries at a given age. It reflects the fertility potential of a woman irrespective of the cause of infertility, even male factor.
Benefits of Testing for Egg Reserve
Testing for egg reserve results should be interpreted with caution. Abnormal values should not be a cause for denying fertility treatment because the predictive power for pregnancy with own eggs is modest. For women, ovarian reserve tests give women insight into the chance of pregnancy with there own eggs. It also may indicate the need to promptly avoid delay in seeking fertility treatment. For reproductive endocrinologists, the tests have value in designing fertility treatment and selecting the most appropriate fertility treatment protocol. They predict response to fertility medications and allow infertility specialists to select treatment protocol and gonadotropin dose. Egg reserve also predicts the number of eggs retrieved for IVF or egg freezing.
Egg Reserve: Egg Number
Although the number of eggs in the ovaries decrease with age there is significant individual variation in initial number endowed in the ovaries and the rate of decrease. Some young women has low egg number and older with large number of eggs. Ovarian reserve tests are used to estimate this number.
Medical history may indicate low egg reserve in women with prior excision of ovarian cysts, endometriosis of the ovaries, women who smoke and with family history of early menopause
Antral follicle count
The number of antral follicles in the ovaries (the structures that contain the eggs) can be seen and counted using vaginal ultrasound. Performed by an experienced reproductive endocrinologist, it can accurately estimate ovarian reserve. Low count e.g <10 in both ovaries points to low reserve.
Day 3 FSH, Estradiol
FSH is produced by the master gland in the base of the brain. Estradiol is made by the follicles themselves. Measured in the second or third day of menstrual cycle, high FSH (>12) of high estradiol (>75) points to low egg reserve.
Antimullerian Hormone (AMH)
AMH is produced by the cells surrounding the eggs in small follicles and is a more direct measure of egg reserve than FSH. It can be accurately measured any day in the cycle with little variations in between cycles. Levels <1.5 ng/dL generally indicates low egg reserve. It correlates well with antral follicle count.
Low egg reserve in few women is due to a genetic cause. Fragile X syndrome is a genetic disease that causes low egg reserve and mental deficiency in newborn males. Chromosomal abnormalities e.g Turner syndrome, translocations are also associated with low egg reserve. Genetic screening is performed using a simple blood test before starting fertility treatment.
Egg Reserve: Egg Quality
What does egg quality means ?
Good quality eggs are chromosomaly normal (has 23 chromosomes). The most important factor that prevents the achievement of pregnancy or leads to early miscarriage is an abnormal egg (has extra or missing chromosome or piece of a chromosome). Many eggs at any age in any woman are abnormal and the normal eggs are the ones that are successful in being fertilized with sperm, implant and achieve a pregnancy. These errors takes place when the original cell that produce the eggs divide to reduce the number of chromosomes to half. The division (meiosis) is many times unequal leading to an egg with an extra or missing chromosome.
Age and egg quality
The ovary releases better quality age earlier in life and lower quality age later, for unknown reason. Female age is the most important indicator for egg quality, chance for spontaneous pregnancy and after fertility treatment. Older women need to try longer to achieve pregnancy and at an increased risk for miscarriage, ectopic pregnancy and delivering a baby with chromosomal abnormalities e.g Down Syndrome. This effect of age become clinically evident at age 30 or even earlier. Age is more important than the number of eggs in the ovaries. Young women with few eggs in the ovary are more successful in getting pregnant than older women with many eggs in the ovary.
Testing for egg quality: PGD
Age is the only available noninvasive method to estimate egg quality. Healthy eggs cannot be identified using any non invasive method. It is possible to identify chromosomal errors in the egg during IVF fertility treatment after biopsy of the first polar body of unfertilized egg or after removing one cell from an embryo after the egg is fertilized then test this material for chromosomal abnormality. This process is called PGD or preimplantation genetic diagnosis. It is important to remember that PGD is not proven so far as method of enhancing fertility potential. It simply detects if the egg or embryo is chromosomaly normal or not but will not make an unhealthy egg healthy.