Originally published: 30.MAY.2018
Last updated: 10.AUG.2023

Our hormones have a major impact on many aspects of our health, including, you guessed it: our fertility. And the follicle-stimulating hormone (or FSH for short) is just one of the primary female hormones that play a critical role in fertility including conceiving and supporting a healthy pregnancy.

The relationship between the follicle-stimulating hormone and fertility can be a complex one, but it doesn’t have to be. Let’s dive into everything you need to know about this crucial hormone including ‘normal’ FSH levels, interpreting FSH test results, and the FSH: LH ratio.

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What is Follicle Stimulating Hormone?

FSH is one of the gonadotrophic hormones associated with fertility in women; the other is the luteinizing hormone (LH). FH is responsible for stimulating the growth of egg-bearing follicles in your ovaries, meaning it helps to control the menstrual cycle and regulate the growth of eggs. It is produced in the pituitary gland and works alongside the luteinizing hormone (LH) to support reproduction.

When to Test FSH Levels in Women

FSH fluctuates during the menstrual cycle, reaching its peak before ovulation. This is why it’s recommended to measure FSH levels on day three of your period via a blood sample. This is the baseline level and is known to provide the most accurate predictions of ovarian reserve. FSH is often measured along with the LH level and estradiol.

In women, FSH can be measured to get insights into:

  • Menstrual irregularities
  • Fertility
  • Ovulation
  • The function of the gonads

If you would like to know more about your fertility, you can check in on your hormone health from the comfort of your home with LetsGetChecked’s Female Hormone Test. The test will provide a broad overview of your hormonal health by looking at Follicle Stimulating Hormone (FSH), Luteinizing Hormone (LH), Prolactin, and Estradiol.

This test is not suitable if you have been taking hormonal contraceptives or hormone replacement therapy within the last three months, as the accuracy of results will be affected.

Related article: How Do You Check Female Fertility From Home?

Ovarian Reserve and FSH

Your ovarian reserve refers to the number of eggs that you have available for fertilization. A high ovarian reserve indicates a good number of viable eggs present in your ovaries. A low ovarian reserve may indicate that you have fewer available eggs. To test ovarian reserve, FSH levels are measured, which correlates inversely with the number of eggs that you have “on reserve.”

Women with a poor ovarian reserve are said to have reached their “oopause". The "oopause" stands for "Poor Ovarian Response", women most commonly reach the "oopause" at the age of 51.

Women with fewer eggs left in comparison to other women of the same age 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 why don’t higher levels mean more eggs?

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 trigger the release of eggs from the ovaries, so the body produces a higher amount of FSH to prompt ovulation. A high FSH means the egg number is reduced, sometimes to levels so low that pregnancy is not possible.

Interpreting FSH Test Results and FSH Levels

Before understanding your FSH test results, keep in mind one thing: your FSH levels alone will not be able to give much information regarding fertility and they are usually looked at alongside estradiol and LH levels.

With that said, below is a general guide to FSH levels and interpreting results

  • -2mlU/ml can indicate hypogonadism
  • 3 mIU/ml–10 mIU/ml are considered healthy levels
  • 12 mIU/ml+ can suggest an impaired ovarian reserve
  • 25mlU/ml+ can confirm ovarian failure and is usually seen in menopausal women

FSH levels can vary depending on a number of factors including age and certain medications - for example, women on birth control usually have low levels of FSH. Elevated FSH levels can also be a result of ovulation-inducing drugs sometimes taken by women with polycystic ovaries (PCOS).

If you have any questions or concerns about your results, be sure to consult with your healthcare provider.

As mentioned, your FSH level is best interpreted in conjunction with your estradiol and LH level. Both a normal FSH and estradiol level indicate that you have a good ovarian reserve.

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 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, even if the FSH is normal, it cannot be assumed that ovarian reserve is normal.

Your FSH: LH ratio should also be looked into. A normal FSH: LH ratio is 1. However, if your FSH level is much higher than your LH level, then this may suggest poor ovarian reserve.

Does a Normal FSH Level Mean you are Healthy?

Not necessarily, if you have a normal FSH level, it does not always mean your eggs are healthy. This is because a high estradiol level can artificially suppress a high FSH level into a normal range, giving you false reassurance. This is why, when you measure your FSH levels, you should also have your estradiol level checked at the same time.

Related articles: Pregnancy Planning? Four Tests You Should Consider Before Starting a Family

If you want to know more about your hormonal health, speak with your healthcare provider who will be able to provide advice and testing. You can also choose to opt for a simple blood test from the comfort of your home with LetsGetChecked’s Female Hormone Test. Our dedicated clinical team will be available to support you and provide guidance on the best next steps.

You must collect your sample on days 3 to 7 of your menstrual cycle. This is because hormone levels vary throughout the menstrual cycle and the reference ranges used by the laboratory are specific to the first week of the cycle.

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Written by Hannah Kingston | Approved by Medical Director Dominic Rowley