Ovarian reserve is the pool of eggs present in the ovaries at any given time. Low ovarian reserve is when there is a physiological decrease in the number of eggs, resulting in an insufficient number to ensure a reasonable chance of pregnancy. Generally, it is caused by aging ovaries. Patients can have diminished ovarian reserve but intact ovarian function.
Females begin life at one of the earliest stages of development with millions of eggs. Unfortunately, a vast majority of them decay before they are ever needed for reproduction. In Utero, there is a rapid multiplication of germ cells starting at six to eight weeks. By the time the female fetus is a 16-20 weeks, she has a peak of six to seven million eggs. This number declines to one to two million eggs at birth, falling even further to 2,50,000 to 5,00,000 eggs at puberty.
At 37 years of age, a woman will only have 25,000 eggs and at menopause less than 1000.
There are three types of eggs in the ovary: a pool of immature eggs, eggs that are selected to mature and prepare for ovulation in a particular cycle, and a pool of atrophic or dead eggs. The eggs are encased in follicles that support and nourish them until they mature, though the vast majority never do so. Every month, a certain number or percentage of immature eggs are selected for maturation. One of these eggs will ovulate and the rest will regress, die and be reabsorbed into the ovary through atresia. The number of eggs selected is dependent on the number of immature eggs in the pool.
Low ovarian reserve is a premature decrease in the number of eggs and can be caused by chromosomal anomalies such as Turner Syndrome, where there the woman does not have two X chromosomes, or gene abnormalities such as Fragile X.
Also ovarian tissue can be destroyed through torsion, surgical removal of part of all of the ovary, ovarian cysts caused by endometriosis, benign or malignant ovarian tumors, radiation or chemotherapy, immunological conditions, pelvic adhesions, or a high body mass indes.
Low ovarian reserve only becomes an issue when a woman has problems getting pregnant. Other women experience this condition in their 30’s and 40’s, but may have had their children earlier in life, so it does not negatively affect them.
IVF success for all age groups is extremely dependent on how many eggs the doctor can obtain at the egg retrieval. A poor responder by definition is a woman from whom three or fewer mature follicles are formed after ovarian stimulation. There is three times less chance of pregnancy if we obtain less than four eggs from poor responders.
Fewer eggs mean fewer embryos to choose for the embryo transfer. Many times poor responders are older so the quality of their eggs is poorer, which decreases the chance of pregnancy and increases the chance of miscarriages. The patient’s response to ovarian stimulation is usually proportionate to their ovarian reserve.
There are several baseline tests used to determine if a woman is a poor responder: