What’s the difference between FSH and AMH?
Written by: Dr. Amy Beckley, PhD, Founder and Inventor of the Proov test — the first and only FDA-cleared test to confirm successful ovulation at home.
Written on 8/30/21
Both FSH and AMH are hormones and markers of your ovarian reserve.
If you are trying to conceive, and especially if you have been considering fertility treatments, follicle stimulating hormone (FSH) and anti-mullerian hormone (AMH) are likely not strangers to you. Both are hormones and both are markers of your ovarian reserve.
But why, you might ask, are there two different measurements for ovarian reserve? Keep reading to learn the difference between FSH and AMH, and if measuring one is better than the other!
What is my ovarian reserve?
Women are born with their entire ovarian reserve, meaning that you are born with all the eggs you will ever have. Unlike men whose sperm replenishes every 72 hours, your eggs are just as old as you are.
This is why as you get older not only does your egg quantity decrease, but the quality of your eggs decreases too, which may impact your fertility and ability to conceive.
According to the American College of Obstetricians and Gynecologists, this is what our ovarian reserve looks like throughout our lifetime, on average:
- About 20 weeks before we’re born: 6 to 7 million eggs
- At birth: 1 to 2 million eggs
- At puberty: 300,000 to 500,000 eggs
- Around age 37: roughly 25,000 eggs
- Around age 51 (the average age of menopause in the United States): roughly 1,000 eggs
While both follicle stimulating hormone (FSH) and anti-mullerian hormone (AMH), give insight into your ovarian reserve, there are two main differences between them. The first is where they’re produced and the second is how they're measured. Let’s dive into each to learn more.
What is FSH and why is it important?
The hormone that stimulates your follicles to grow and mature is appropriately named follicle stimulating hormone (FSH). Your FSH levels will rise temporarily during the first half of your cycle to encourage your ovaries to produce mature follicles and eggs in preparation for ovulation.
FSH is the fuel to your ovaries. When your ovaries have many eggs left (i.e. a normal ovarian reserve) and are working properly, they won’t need as much FSH to stimulate them. However, the less eggs you have left, the more FSH that will be required to stimulate the follicles.
At the beginning of your cycle your FSH levels will be low, ideally under 10. When you’re younger, you’ll also have many premature follicles ready to grow and produce an egg. During your period, your brain will send a signal to your ovaries that it’s time to start preparing for ovulation and a small amount of FSH will stimulate them.
Your ovaries will not have an issue recruiting the follicle that will eventually grow, mature, and ovulate because it will have plenty to choose from, meaning they also won’t require too much FSH. Easy peasy!
However, as you get older and your ovarian reserve diminishes, meaning you will also have a lower number of follicles to start each cycle. Your ovaries will have a limited choice of follicles to recruit from and will need more fuel (FSH) to make that follicle grow. High FSH levels at the beginning of your cycle can signify your ovaries are struggling to recruit and grow follicles.
High FSH levels at the beginning of your cycle can signify that your ovaries are struggling to recruit and grow follicles.
What is AMH and why is it important?
AMH is produced throughout your life by the outer layer of your premature follicles. These are the follicles in your ovaries that are not yet ready to grow or release an egg.
When you are younger and have many eggs left, your AMH levels will be high. As you age, you have less follicles and eggs left (meaning a smaller ovarian reserve), and your AMH levels will be lower.
After AMH was discovered by scientists in the 90s, many people believed AMH tests were a key assessment of fertility. However, recent years studies have proven that while AMH is a good marker of ovarian response to fertility medications (such as ovarian stimulation drugs), it has little impact on natural conception.
This is because in medicated cycles, such as in-vitro fertilization (IVF), doctors try to recruit as many follicles and eggs as possible in that single cycle. The more eggs you have to recruit, the better your chances are of getting a healthy one.
In natural cycles where medication is not used, only one follicle ovulates, so the number of follicles you’re not trying to mature as many as possible. Of course, if you or your doctor thinks understanding your AMH levels could be helpful we always believe you can be empowered with more information about your body!
What’s the difference between FSH and AMH?
As we previously mentioned, while FSH and AMH both give insight into your ovarian reserve, there are two key differences between the two hormones.
The first is where and how they’re produced. You’ll remember that FSH stimulates your ovaries to produce follicles, while AMH is produced by premature follicles that aren’t yet ready to release an egg.
The second difference is how these hormones are tested. FSH can be measured via blood or urine, while AMH can only be measured via blood. Additionally, we’ve found that AMH tests can be more expensive than urine-based FSH tests.
Both FSH and AMH should be measured at the beginning of your cycle. If you’re testing these hormones via blood, you should ideally take your test on cycle day 3. If you are measuring FSH levels via urine with the Proov FSH test, we recommend testing on cycle days 5, 7, and 9, as it takes FSH a few days to reach your urine and studies show it can fluctuate day by day.
If you are measuring FSH levels via urine with the Proov FSH test, we recommend testing on cycle day 5, 7, and 9.
Is one ovarian reserve hormone better than the other?
The short answer to this question is no — FSH isn’t better than AMH or vice versa. Depending on your situation you may want to consider one over the other, for example if you’re looking for an at-home testing option you’d likely turn to a urine-based FSH test first. On the other hand, if you’re undergoing IVF, your doctor will likely recommend an AMH test.
In fact, both FSH and AMH have their limitations. FSH is typically measured with estrogen, as elevated estrogen levels can falsely lower FSH levels. This means that your FSH levels may actually be much higher than they are reading on your test results.
Additionally, many doctors recommend testing FSH and LH together in order to establish an LH to FSH ratio. An abnormal LH:FSH ratio can be a sign of PCOS.
The last thing we’ll mention is that one single test — FSH, AMH, or whatever it may be — is not indicative of your overall fertility status. It’s important to get a more holistic view of your cycle in order to have the best possible chance at conception.