Here's Why an FSH Test Is Important for Monitoring Your Fertility

People going through fertility testing often hear about follicle-stimulating hormone (FSH) and may wonder what a normal FSH level is to get pregnant. As part of a basic fertility workup, your doctor will likely order blood work to check your FSH levels. Sometimes called the day 3 FSH test, this is a simple blood test meant to measure the amount of FSH in your bloodstream. While normal levels vary from person to person, the typical healthy range is between 4.7 to 21.5 mIU/mL.

FSH testing has traditionally been used to evaluate ovarian reserves, though that’s not the only purpose of testing. Ovarian reserves refer to the number and quality of eggs left in the ovaries. High FSH levels may indicate diminished ovarian reserves, which can make getting pregnant more difficult. Fertility treatments may not be as effective as stimulating ovulation or follicle development.

However, research has found that calculating FSH levels is not the best way to check ovarian reserves. One big problem with FSH testing is that getting a normal value doesn’t ensure that your ovarian reserves are good. You can have normal FSH levels and still face age-related infertility. You may also still end up responding poorly to fertility treatment. Learn more about what FSH levels can—and can not—tell you about your fertility.

What FSH Does in the Body

To understand FSH level testing, it helps to know how the hormone works in the body. Its job is to tell the oocytes (premature eggs) in your ovaries to begin growing. Each oocyte is contained within a follicle, or fluid sac. The growth and development of the oocytes is the first part of the process that will, ideally, lead to ovulation.

FSH works on a feedback loop with estrogen. As FSH tells the eggs in your ovaries to grow, the eggs release estrogen in response. As the follicles (or eggs) get bigger, they release more estrogen. The higher levels of estrogen stimulate your reproductive system to slow down the release of FSH.

In other words, FSH levels naturally drop as the follicles get bigger and eggs in the ovary mature. If the eggs don’t start to mature and release estrogen, then FSH levels won’t drop. In fact, the body will release more and more FSH in an attempt to stimulate egg development.

High FSH Levels

If FSH levels are abnormally high, this implies that the body needs more FSH to stimulate egg maturation and ovulation. This could indicate a less than ideal quality and quantity of eggs in the ovaries. This is a normal part of aging and is more common in women age 38 or older. However, even young people can have high FSH levels. For example, a person in their 20s may have high FSH levels if they're experiencing primary ovarian insufficiency (premature ovarian failure).

One study had women with high FSH levels attempt IVF treatment. The researchers found that some women responded well to treatment, while others did not. Those who did respond had decent pregnancy success rates. The researchers concluded that the best way to know if fertility drugs will work is to try them. FSH levels alone can’t predict who will have success and who won’t.

Low FSH Levels

FSH levels can also be abnormally low. This is usually in combination with low luteinizing hormone (LH) levels and may indicate a problem with the functioning of the pituitary gland or hypothalamus, which are two parts of the brain that play important roles in ovulation.

Why Normal FSH Levels Are Important

High levels of FSH may indicate poor ovarian reserves. In layman’s terms, poor ovarian reserves means that both the quantity of eggs and their quality is low.

FSH levels are also used to evaluate whether in vitro fertilization (IVF) treatment or injectable fertility drugs could be effective. Women with high FSH levels or poor ovarian reserves are less likely to respond to high doses of fertility drugs. Depending on how high FSH levels are, some doctors will discourage IVF treatment because the cycle is more likely to be canceled or fail.

Why? When FSH levels are abnormally high, it's because eggs are not maturing with normal levels of FSH. The body will try to fix the problem by increasing FSH. With IVF or injectable fertility drugs, the hormone FSH is being injected to stimulate your ovaries.

If your ovaries aren’t responding to your natural FSH, they are also unlikely to respond to injected FSH. In a woman with good ovarian reserves, injected FSH will lead to strong egg growth in her ovaries. In a woman with poor ovarian reserves, the ovaries will not respond as well.

Still, high FSH levels don’t necessarily mean you can’t conceive with your own eggs. Your doctor may just need to try a different protocol. If a doctor tells you that IVF is not possible without using an egg donor, get a second opinion before moving forward. Another doctor may have an approach that could work better for your individual situation and needs.

How an FSH Blood Test Is Performed

The blood test is like any other blood test. Your doctor will tell you when to have the test done. For the test, a nurse will draw blood from a vein in your arm. You may feel a small pinch, but the test is generally pain-free and simple.

There are also at-home FSH tests available to purchase, though it's worth noting that they're not as reliable. These work similarly to a pregnancy test in that you test your hormone levels with urine. The test could tell you if your levels are too high, but it may still give you a "normal" indication even if a fertility specialist would have declared your levels higher than normal.

Why FSH Levels Are Tested on Day 3

The timing for FSH testing is crucial. Because FSH levels vary throughout the menstrual cycle, the normal range varies by day. For basic fertility testing and to evaluate ovarian reserves, you need to have the blood test on day 3 of your menstrual cycle (day 1 is the day your period begins).

However, most doctors are OK with the test being done on any day between days 2 to 4. FSH levels may also be checked at another time during the menstrual cycle, but this isn't a common approach, as results may not be as accurate.

One reason why FSH testing is considered less useful than other ovarian reserve testing methods is the requirement that it has to be tested at a particular time. Also, FSH levels can vary not only throughout the menstrual cycle but also from cycle to cycle. You can get a normal test value one month and an abnormal test value the next.

What Are Normal FSH Levels?

A study on day 3 FSH levels and IVF outcomes showed that women with day 3 FSH levels lower than 15 mIU/ml had a better chance of pregnancy achievement per IVF attempt when compared to women with FSH levels between 15 mIU/ml and 24.9 mIU/ml. For women with day 3 FSH levels over 25 mIU/ml, pregnancy rates per attempt were even lower.

Sometimes FSH levels are normal, but day 3 estradiol levels are abnormally high. If your estradiol is high, but your FSH levels are normal, you may still have poor ovarian reserves. High estradiol levels can suppress FSH, because FSH and estradiol work together. When estrogen levels are high, the body lowers FSH in response. If your estrogen levels are high, your FSH levels will naturally drop, but this doesn’t mean your ovaries are responding to the FSH.

Sometimes, women want their FSH levels tested in order to get an idea of whether they should start trying to have a baby soon or if they have more time. If you get a normal result, you may think you don’t have to worry about age-related infertility.

Unfortunately, this isn’t true. One study found that women could have normal FSH levels well past the age that difficulty getting pregnant would begin based on age. While high FSH levels can be a bad sign, normal FSH levels aren’t necessarily a sign that you can wait a few more years before trying to have a baby.

Alternatives to FSH Level Testing

Day 3 FSH level testing is only one way to measure ovarian reserves. Your doctor is likely to look at a variety of indicators before making a diagnosis.

Your doctor may also test your Anti-Müllerian hormone (AMH) levels to help diagnose polycystic ovary syndrome (PCOS) and ovarian reserves. Like the FSH test, AMH is also a simple blood test. But AMH levels can be tested at any time during the menstrual cycle. Also, research has found that AMH more accurately determines potential ovarian reserves.

Another test is an antral follicle count ultrasound exam. This is a transvaginal ultrasound exam where a technician counts the number of follicles of a specific size in the ovaries. One downside of antral follicle testing is that the results can vary based on the skill of the technician. However, the test is worthwhile and can give your doctor a better idea of your potential ovarian reserves.

A Word From Verywell

When looked at alone, your FSH levels can’t tell your doctor much. As a result, FSH levels have to be looked at alongside estrogen and LH levels. Also, while high FSH levels may indicate lower odds of fertility treatment success, having normal FSH levels won’t ensure treatment will go smoothly. When it comes to evaluating ovarian reserves, FSH testing isn’t the best method. But your doctor can help you determine what type of testing may be appropriate for your situation.