Day 3 FSH Levels Test

What FSH Levels Can and Can't Tell You About Your Fertility

Close up of pathologist in rubber gloves holding blood sample
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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 follicle stimulating hormone in your bloodstream. 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. If a woman’s FSH levels are high, she may have diminished ovarian reserves. It may be more difficult for her to get pregnant, and fertility treatments may not be as effective as stimulating ovulation or follicle development.

However, research has found that FSH levels are not the best way to test for 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 or respond poorly to fertility treatment.   

What FSH Does in the Body

To understand FSH level testing, it helps to know how the hormone works in the body. FSH’s job is to tell the oocytes, or premature eggs, in your ovaries to begin growing. Each oocyte is contained within a follicle or little 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. So, in other words, FSH levels will 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, your body will release higher and higher levels of FSH in a desperate attempt to stimulate egg development.

If FSH levels are abnormally high, this implies that your body requires much more FSH to stimulate egg maturation and ovulation. This could indicate that the quality and quantity of eggs in your ovaries are less than ideal. This is a normal part of aging and is more common in women age 38 and up. However, even young women can have high FSH levels. For example, with primary ovarian insufficiency (premature ovarian failure), a woman in her 20s may have high FSH levels.  

FSH levels can also be abnormally low. If FSH levels are abnormally low, usually in combination with low LH, this may indicate a problem with the functioning of the pituitary or hypothalamus, two parts of the brain which play an important role in ovulation.

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. That said, most doctors are OK with the test being done on any day between days 2 to 4. The first day of your cycle is the day your period begins.

FSH levels may also be checked at another time during the menstrual cycle, but this is uncommon.

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

Why Are FSH Levels Important

High levels of FSH may indicate poor ovarian reserves. In layman’s terms, it means that the quantity and quality of your eggs are low. While high FSH levels do indicate that you may have more difficulty getting pregnant, they don’t mean that you cannot get pregnant. They are just one factor to be taken into consideration.

FSH levels are also used to evaluate whether 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 a couple from going forward with IVF treatment because the cycle is more likely to be canceled or fail.

Think of it this way: When your FSH levels are abnormally high, this is because the eggs in your ovaries are not maturing at normal levels of FSH. Your body tries to fix the problem by increasing FSH, until (hopefully) the eggs mature. With IVF or injectable fertility drugs, the hormone FSH is being injected to stimulate your ovaries. But just like your ovaries aren’t responding to your natural FSH, they also are unlikely to respond to injected FSH.

In a woman with good ovarian reserves, FSH injected hormone will lead to strong egg growth in her ovaries. In a woman with poor ovarian reserves, the ovaries will not respond as well.

All that said, 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 on. Another doctor may have an approach that could work for you.

How Is An FSH Levels Blood Test Done

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 essentially pain-free and simple.

There are also at-home FSH tests sold. These work a lot like a pregnancy test, in that you test your level with urine. The test will indicate if your levels are "too high." You may be tempted to try these tests, but they are not reliable. You can get a "normal" indication even if a fertility specialist would have declared your levels higher than normal. Don't waste your money. 

What Are Considered to Be Normal FSH Levels?

The normal range will vary between labs. A normal value at one clinic may be abnormally high in another. You need to speak to your doctor for an accurate interpretation. Also, comparison with your LH levels and estrogen levels (specifically estradiol, or E2) is required, to get the entire picture.

With that said, a study on day 3 FSH levels and IVF outcomes showed that women with day 3 FSH levels less 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. This is because FSH and estradiol work together in a feedback loop. 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.

What Does It Mean the Levels Are High?

Generally, high FSH and/or estradiol may indicate poor ovarian reserves. This may suggest that fertility drugs will be less effective.

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

Do Normal FSH Levels Mean You Can Wait to Have a Baby?

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. This is part of the appeal of at-home FSH tests. If you get a normal result—people mistakenly think—then 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 a "good" sign. It doesn’t mean you have more years to wait before having a baby.

Alternatives to FSH Level Testing

Day 3 FSH levels are 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 AMH levels. Anti-Müllerian hormone can be used to help diagnosis PCOS and ovarian reserves. Like the FSH test, AMH is also a simple blood test. But even better, your AMH levels can be tested at any time during your cycle. Also, research has found that AMH more accurately determines potential ovarian reserves.

Another test that can be used alongside FSH levels is an antral follicle count ultrasound. This is a transvaginal ultrasound 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. FSH levels have to be looked at alongside estrogen and LH hormone levels. Also, while high FSH levels may indicate lower odds of fertility treatment success, normal FSH levels don’t ensure treatment will go smoothly. When it comes to evaluating ovarian reserves, FSH isn’t the best method. Your doctor should also test your AMH levels and possibly order an antral follicle count ultrasound. 

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