What is FSH ( follicle stimulating hormone)

FSH is an acronym which stands for Follicle Stimulating Hormone. Hormones act as messengers - they are chemicals in your body that are made in one place and are used in another.

About FSH

  • As the name suggests, FSH is responsible for stimulating the growth of the egg-bearing follicles in your ovaries
  • It is one of the two gonadotropins (so called because it stimulates the gonads), the other being its partner, LH, which stands for luteinising hormone
  • LH and FSH are secreted by the pituitary gland, a small pea-shaped gland below the base of your brain
  • FSH levels vary during the menstrual cycle and will peak prior to ovulation
  • This is why the level of FSH in your blood is best measured on Day 3 , and this is called the baseline (basal) level
  • FSH blood tests are generally performed on the second or third day of your menstrual cycle, when they provide the most accurate predictions of ovarian reserve
  • The FSH is often measured along with the LH level; and estradiol .

Ovarian Reserve and Follicle Stimulating Hormone

  • Your ovarian reserve refers to the number of eggs that you have available for fertilization
  • A high ovarian reserve usually indicates a good number of viable eggs present in your ovaries
  • A low ovarian reserve may indicate that you have fewer available eggs
In order to test ovarian reserve, we measure your FSH level , which correlates inversely with the number of eggs that you have "on reserve" in your ovaries - your ovarian reserve. Women with a poor ovarian reserve are said to have reached their oopause.

When More is Not Always Better

Women with poor ovarian reserve will have high FSH levels. Some women find it difficult to understand why FSH levels are high in women with poor quality eggs. Intuitively, more is better, so higher levels should mean better eggs, shouldn't it ?

As one patient asked me, " If FSH stands for Follicle Stimulating Hormone, and I have high levels of FSH, then doesn't that mean that I have the ability to stimulate lots of follicles ? A high FSH should mean that I should have lots of eggs ! "

Let's look at the basic biology. If the ovary has many eggs, the FSH in a woman's blood is low because the body doesn't need to produce much FSH to induce normal ovulation. However, if the egg number is low, the body needs to work harder to produce ovulation, so it increases the amount of FSH in an effort to push the ovaries.

What is a good level?

A high FSH means the egg number is reduced, sometimes to levels so low that pregnancy is not possible.What is a good level? Well that depends on each individual lab. For most centers, anything over 12 mIU/ml is considered poor . In fact, some centers will not give fertility treatment to those over 12 because the odds of pregnancy become low.

Interpreting Levels of Follicle Stimulating Hormone

  • A normal FSH level is usually between 3 mIU/ml - 10 mIU/ml. Levels of more than 12 mIU/ml are worrisome and suggest impaired ovarian reserve
  • Levels of more than 25 confirm ovarian failure and are found in menopausal women
  • FSH levels can also be artificially raised by ovulation inducing drugs such as clomiphene citrate (clomid)
  • Low levels of FSH (less than 2 mIU/ml) are found in a condition called hypogonadotropic hypogonadism. Women on birth control pills as well as pregnant women also have low levels of FSH
  • The FSH level is best interpreted in conjunction with your estradiol level
  • Estradiol is one of the estrogens produced by the ovaries
  • Estradiol levels above 75 pg/ml on Day 3 may indicate a poor ovarian reserve
  • In some women , a high baseline estradiol level (because of poor ovarian reserve) can artificially suppress the FSH level, so that it appears to be normal, thus misleading the doctor into believing that the ovarian reserve is normal
  • This is why it's a good idea to measure the estradiol level when checking the FSH level on Day 3
  • If the estradiol level is high, then even if the FSH is normal, we cannot assume that ovarian reserve is normal
  • A normal FSH and estradiol level probably indicate that you have a good ovarian reserve
  • Elevated FSH levels may suggest impaired ovarian reserve and may imply that you consider begin treatment right away
  • High levels of FSH may indicate that you should consider using an egg donor. Your eggs may not be fertile

The Age Factor

It is also necessary to consider age when undergoing fertility treatment. Age is an excellent predictor of both ovarian reserve and conception rates. Women over the age of 43 have a smaller chance of becoming pregnant than women under the age of 43, no matter what their FSH levels. This means that younger women with poor FSH levels may still want to try using their own eggs before seeking a donor.

Other tests for ovarian reserve

  • The other tests for ovarian reserve include testing for inhibin levels; and AMH levels
  • Vaginal ultrasound scanning is also useful for measuring the antral follicle count.

If any one of the tests for ovarian reserve was truly accurate then it would eliminate the need for the others ! The fact that there are so many (FSH, oestradiol, AMH, antral follicle count, inhibin) suggests none of them are truly reliable. If one test were the right one then that is the one we'd all be given and it would tell us the answer!

Please do remember that doctors do not treat numbers - we treat patients, so don't obsess over just one number is isolation.The final proof of the pudding is in the eating - and your response to superovulation is the best way of assessing your ovarian reserve. If you grow eggs well, then you should not worry about your "numbers" !

FSH and LH levels in patients with PCOD

  • We often measure both FSH and LH levels. Normally, the ratio is 1, which means the FSH level and LH level are approximately the same
  • In patients with polycystic ovarian disease (PCOD), this ratio is reversed; and patients with PCOD typically have a high LH level and a normal FSH level
  • This is called a reversal of the FSH:LH ratio; and in patients with PCOD it is 2 or more

FSH as a test versus FSH as a medication

Measuring the level of FSH in your blood is a very useful diagnostic tool .
You also need to remember that the FSH hormone is also used as a medication to help in superovulation during your IVF treatment. Brand names include Follistim and Gonal-F.

Authored by : Dr Aniruddha Malpani, MD and reviewed by Dr Anjali Malpani.