Ovarian Reserve and FSH
FSH, a hormone produced by the pituitary gland in the brain, is released into the bloodstream and travels to the ovary where it stimulates immature follicles containing microscopic oocytes to eventually develop a mature oocyte (egg). Early in the menstrual cycle, if the blood level of FSH is high, it indicates that the pituitary is working hard to stimulate the ovaries, therefore, the number and perhaps quality of the remaining eggs is decreased. FSH is tested on day 2 or 3 of your cycle to provide a baseline measurement. An elevated FSH level above 8 might suggest that a woman is starting to experience the loss of her ovarian reserve. Menopausal women show FSH levels that are above 40. However, there are several variables, and as with many issues surrounding infertility, it has much to do with age.
Proper interpretation of FSH levels requires a simultaneous measurement of blood estrogen (estradiol) levels. Estradiol is made by the ovary, enters the blood stream and travels back to the brain (pituitary) to help regulate FSH release. Early in the cycle, day 2 or 3, it should be less than 60. A high level of estradiol, above 80, indicates that estradiol is suppressing the pituitary and providing an inaccurate FSH reading.
Several studies have set out to determine whether women with elevated basal FSH levels should be excluded from fertility treatment. A comprehensive study in the United Kingdom analyzed over 2000 patients for four years undergoing IVF treatment. Although it found no significant correlation between FSH levels and fertilization rates or miscarriage rates, the pregnancy rates and live birth rates were lower among women with higher FSH levels. Elevated FSH levels were also associated with more frequent cycle cancellation, need for larger amounts of stimulation medication, and lower numbers of eggs and embryos with fewer embryos transferred. However younger women, even with high FSH levels, had significantly greater live birth rates compared to older women with normal FSH levels. Again, age matters, despite a normal FSH value.
A normal FSH reading, although reassuring, may be indicative of egg quantity but not necessarily quality. The follicles may be producing mature eggs, however, the quality of those eggs may not be adequate. This is especially true for women over 40 years old. Another caveat is that most women have variable FSH readings from one cycle to another. The best indicator of treatment response, however, is typically the highest FSH reading. There is no benefit, therefore, in repeated testing of FSH over several cycles and choosing to undergo an IVF cycle when the FSH is normal.