What is FSH and when should
it be tested?
Cycle Day 3 Follicle Stimulating Hormone: FSH
Follicle stimulating hormone (FSH) is one of the most important hormones involved in the menstrual cycle. FSH is secreted by the pituitary gland in the brain. It is the primary hormone involved in ovulation.
To determine if a woman has a good number of healthy eggs left in her ovaries, a serum FSH level can be measured. The test is usually performed on cycle day 3 but it can also be performed on day 2, 3, or 4 of a woman’s menstrual cycle. (The first day of menstrual bleeding – spotting does not count- is considered Cycle Day 1. Therefore Cycle Day 3 is the third day of a woman’s period.)
You can think of the action of FSH as similar to what happens when you step on the gas pedal in the car to get going. In this analogy, FSH is the gas, and the pituitary gland is the gas pedal releasing FSH to get a follicle “going” at the beginning of every menstrual cycle.
As women approach menopause, their baseline FSH level will gradually increase. When a woman goes into menopause she is essentially running out of eggs and estrogen production in her ovaries. Sensing a low estrogen environment, the brain releases more FSH from the pituitary gland in an attempt to stimulate the ovaries to produce a mature follicle and more estrogen.
In most laboratories, normal values of cycle day 3 FSH are less than 13 mIU/ml although there is some variation among different labs in what is considered the upper limit of normal. When a woman runs out of follicles capable of responding, cycle day 3 FSH will be quite high (over 30-40 mIU/ml) and she will stop having menstrual periods. Elevated FSH levels indicates a reduction in the quality as well as the quantity of eggs. This is reflected in higher miscarriage rates seen among older women.
Female Reproductive System
- Uterus – uterine anatomy and menstrual cycle
- Fallopian Tubes – tubal anatomy and functions
- Fallopian Tube Length – Fallopian tube length from the Tubal Reversal Message Board
- Ovaries and Ovulation – ovulation requires egg maturation and release from the ovary
- Ovulation monitoring – ovulation predictor kits and basal body temperature charts
- Cycle Day 3 FSH – Follicle Stimulating Hormone and when should it be tested
- Early Pregnancy Signs – and When They Occur