One of the greatest threats to fertility for females is advancing age. Beginning in the mid-30s, the egg supply, or egg “reserve,” for women begins to drop at an increasing pace. Ovarian reserve is a rough estimate of the number of eggs a woman has remaining for the future.
Female age is important in considering the probability for pregnancy because it is linked to egg quality, which directly affects embryo quality. A decrease in both the quantity and quality of the eggs (below threshold levels) is known as diminished ovarian reserve.
Tests of ovarian reserve are done be fertility specialists to estimate the remaining egg supply and to help us choose the most efficient course of treatment. The three best tests for ovarian reserve are:
- Antral follicle count (AFC): a vaginal ultrasound is done during the first few days of the menstrual cycle to measure the number of early stage (2-9mm) follicles present. In general, ovarian size and antral follicle count decrease with age. An AFC of 10 or more indicates good ovarian reserve while an AFC of 5 or less indicates diminished ovarian reserve.
- Antimullerian hormome (AMH): a blood test that measures a hormone secreted by specialized cells within preantral and small antral (less than 4mm) follicles. It can be measured on any day of a woman’s cycle. It reflects the size of the remaining egg supply. Women with many small follicles (i.e. polycystic ovaries) have high AMH levels while women with few remaining follicles (i.e. peri-menopause) have low (even undetectable) AMH levels.
- FSH (Follicle Stimulating Hormone) and Estradiol levels: blood tests performed typically on day 2-4 of the menstrual cycle. FSH is secreted by the pituitary gland and travels to the ovary to encourage follicle growth (and thus estrogen). For a woman with a diminished supply of follicles, the ovary is more resistant to stimulation and her FSH levels will rise. Typically, FSH levels above 10 mIU/ml indicate a decline in ovarian function.
Ovarian reserve tests cannot tell us directly about egg quality. Female age is the best indicator we have at this time for egg quality. Women with better ovarian reserve testing will tend to have better response to ovarian stimulation for IVF and have more eggs retrieved. In general, having more eggs with IVF gives a higher success rate.