FSH is made by your pituitary gland, a small gland at the base of your brain. Its job is to tell your ovaries to grow and mature an egg each month.
Early in your cycle, FSH rises to kick-start a group of follicles (the fluid-filled sacs that each contain an egg). One follicle usually becomes dominant, and it's this follicle that releases an egg at ovulation.
Your ovaries and pituitary gland are in constant conversation. As your follicle grows, it produces oestrogen, which signals back to the pituitary gland to slow FSH production. This feedback loop is what keeps your cycle running smoothly.
When this system starts to struggle, usually because there are fewer eggs left to recruit, your pituitary gland has to work harder. It releases more FSH to try to get a response. That's why an FSH test can offer a window into how your ovaries are functioning.
There isn't a single "normal" FSH number. Your level naturally shifts across your menstrual cycle, so the result only means something when it's read alongside the day it was taken.
In the UK, FSH is usually tested on day 2 to day 4 of your cycle, counting from the first day of your period. This is when your levels are at their most stable and easiest to interpret.3
NHS laboratory reference ranges for women who are still menstruating are roughly:
Early follicular phase (day 2 to 4): 1.5 to 10 IU/L
Mid-cycle, around ovulation: 7 to 20 IU/L
Luteal phase, after ovulation: 1.5 to 8 IU/L¹
A result in the lower part of the early follicular range is generally seen as reassuring. It suggests your pituitary gland isn't having to push hard to stimulate your ovaries.
It's worth saying clearly: a normal FSH result doesn't guarantee pregnancy, and a result slightly outside the range doesn't mean you can't conceive. FSH is one piece of information your GP will consider alongside your age, your cycle history, and any other tests.
A raised FSH level, particularly on day 2 to 4 of your cycle, can suggest your ovaries are having to be prompted harder to produce a mature follicle. This is often linked to a lower number of remaining eggs, sometimes called reduced ovarian reserve.
If you're under 40 and your periods have become irregular or stopped, a raised FSH level may be part of investigating premature ovarian insufficiency (POI). NHS guidance defines this as an FSH concentration above 25 IU/L, with repeat testing after 4 to 6 weeks if there's diagnostic uncertainty. This repeat testing matters, because FSH can fluctuate from one cycle to the next, and a single high reading isn't enough on its own to confirm anything.²
A high FSH result isn't a diagnosis by itself, and it isn't a reason to panic. It's a prompt for further conversation with your GP about what it means for you specifically.
A very low FSH level can point towards a different issue: the pituitary gland itself isn't sending out enough signal. This can happen with certain pituitary or hypothalamic conditions. It can also be affected by things like very low body weight, intense exercise, or high stress levels.
Hormonal contraception can also suppress FSH, which is why your GP will usually ask what, if anything, you're taking before requesting the test.
Once you're pregnant, FSH is naturally suppressed. Rising hormone levels from the pregnancy itself send a strong signal back to your pituitary gland, telling it to stop stimulating your ovaries, since there's no need to grow another follicle. NHS pathology guidance lists pregnancy as one of the recognised causes of a low or suppressed FSH result.³
In other words, a low FSH reading during pregnancy is expected and not something to worry about. It's a completely different context from a low FSH result before conception, when it might prompt further questions.
FSH isn't usually the first test offered. NHS guidance is that if you have regular periods, your GP will typically start by testing progesterone to check whether you're ovulating. If your periods are irregular, you'll usually be offered a test for FSH and other hormones that stimulate the ovaries.
NHS guidance is to see your GP if you haven't conceived after a year of regular unprotected sex. If you're 36 or over, or you have a reason to be concerned about your fertility, it's worth booking in sooner rather than waiting.⁴
Some fertility clinics also offer FSH testing as part of a broader ovarian reserve check, often alongside AMH (anti-Müllerian hormone) and an ultrasound antral follicle count. The UK's fertility regulator, the HFEA, notes that FSH and AMH testing can give an indication of fertility but can't guarantee an outcome either way.⁵
Try not to read too much into a single number before you've spoken to your GP. Here's what usually happens next.
Repeat the test. FSH can vary between cycles, so one reading is rarely the full picture.
Bring your cycle history. Note any changes to your periods, as this helps your GP interpret the result properly.
Ask what it means for your specific situation. Your age, your partner's fertility, and your overall health all factor into next steps.
Consider a referral. If results suggest reduced ovarian reserve or POI, your GP may refer you to a specialist fertility service.
Whatever the result, remember that fertility testing is about gathering information, not delivering a verdict. Many people with results outside the "typical" range go on to conceive, and many factors beyond FSH play a role in your chances each cycle.
Understanding your FSH result is one part of the picture. Timing, and giving sperm the best possible starting point, is another.
The twoplus Applicator is designed to deposit sperm close to the cervix, working with your body's natural process rather than replacing it. It's a form of intracervical insemination (ICI) that couples can use at home, in their own time, alongside continuing to work with their GP on any fertility investigations. It isn't a treatment for a high or low FSH result, and it doesn't change your ovarian reserve. What it may do is give you a more comfortable, private way to try each month while you and your GP work through what your test results mean.
If you're still waiting on results, or your GP has suggested trying for a little longer before further tests, the Applicator can be one part of your approach at home. If your results point towards a specialist referral, it can also be used alongside that care, not instead of it. Always discuss your individual circumstances with your GP, particularly if test results suggest a specific fertility condition.
Whatever your FSH result shows, you don't have to navigate it alone. Talk to your GP about what your numbers mean for you, and consider how tools like the twoplus Applicator can support your at-home experience while you do.
Is there an ideal FSH level for getting pregnant? There isn't one single ideal number. A result in the lower part of the early follicular range (roughly day 2 to 4 of your cycle) is generally seen as reassuring, but your GP will interpret it alongside your age and cycle history.
Can FSH levels change from month to month? Yes. FSH can fluctuate between cycles, which is why a single result is rarely used to make a diagnosis on its own. Doctors often repeat the test before drawing conclusions.
Does a high FSH level mean I can't get pregnant? No. A raised FSH result suggests your ovaries may need more stimulation to produce a mature egg, which can make conceiving take longer. It doesn't rule pregnancy out.
When should I ask my GP for an FSH test? NHS guidance suggests seeing your GP if you haven't conceived after a year of regular unprotected sex, or sooner if you're 36 or over or have other fertility concerns.⁴
Is FSH testing different once I'm already pregnant? Yes. FSH is naturally suppressed during pregnancy, so a low reading at that stage is expected and isn't a cause for concern.
North West London Pathology (NHS) – Follicle stimulating hormone (FSH) reference ranges: https://www.nwlpathology.nhs.uk/test/follicle-stimulating-hormone-fsh/
NHS England Genomic Medicine Service, Genomics Education Programme – Premature ovarian insufficiency: https://www.genomicseducation.hee.nhs.uk/genotes/knowledge-hub/premature-ovarian-insufficiency/
University Hospitals of North Midlands NHS Trust – Follicle Stimulating Hormone (FSH): https://www.uhnm.nhs.uk/our-services/pathology/tests/follicle-stimulating-hormone-fsh/
NHS – Diagnosis of infertility: https://www.nhs.uk/conditions/infertility/diagnosis/
Human Fertilisation and Embryology Authority (HFEA) – A-Z fertility glossary: https://www.hfea.gov.uk/about-us/a-z-fertility-glossary/
