Hormone blood tests can show whether ovulation is happening and whether another hormone, such as thyroid or prolactin, may be getting in the way. Several of them depend on the day of your cycle, and each lab has its own normal range, so results need to be read in context.
Why hormones are tested
Hormones are chemical messengers. A small gland at the base of the brain, the pituitary, sends signals to the ovaries each month. The ovaries respond by growing a follicle (a small fluid-filled sac that holds an egg), releasing the egg, and preparing the lining of the uterus.
Blood tests can show how well this conversation between the brain and the ovaries is going. They help a doctor answer two main questions: is ovulation happening, and is anything else, such as the thyroid, affecting it?
Not everyone needs every test. Your doctor should choose tests based on your cycles, symptoms and history, and explain why each one is suggested.
Timing matters
Hormone levels change a lot through the menstrual cycle. Day 1 is the first day of full bleeding, not spotting. A result taken on the wrong day can look unusual when nothing is wrong.
| Test | What it is | Usually taken |
|---|---|---|
| FSH (follicle-stimulating hormone) | Pituitary signal that tells follicles to grow | Early in the cycle, day 2 to 5 |
| LH (luteinising hormone) | Pituitary signal that triggers ovulation | Early in the cycle, day 2 to 5 |
| Oestradiol | A form of oestrogen made by growing follicles | Early in the cycle, day 2 to 5 |
| Progesterone | Hormone made after an egg is released | Mid-luteal: about 7 days before the next expected period |
| TSH (thyroid-stimulating hormone) | Shows how the thyroid is working | Any day |
| Prolactin | Hormone linked to breast milk production | Any day, often in the morning |
If you are asked to have an early-cycle test and your period comes on a Sunday or a holiday, ask the lab or your doctor which day to go instead.
What each test can show
FSH. When the ovaries have fewer follicles left, the brain often sends a stronger FSH signal. So a raised early-cycle FSH can suggest a lower ovarian reserve. FSH can vary quite a lot from one cycle to the next, and it is less reliable than AMH or a follicle count for estimating reserve. A very low FSH, together with low LH, can point to the pituitary not sending enough signal.
LH. LH is read alongside FSH. It is sometimes higher in people with polycystic ovary syndrome (PCOS), but it is not used on its own to diagnose PCOS. LH also surges briefly just before ovulation, which is what home ovulation kits detect.
Oestradiol. Early in the cycle, oestradiol is mainly useful for reading an FSH result correctly. A high early oestradiol can push FSH down and make it look better than it is.
Progesterone. After an egg is released, the empty follicle makes progesterone. A clearly raised mid-luteal progesterone suggests ovulation happened in that cycle. If your cycles are long or irregular, the test may need repeating, because it is hard to know when "7 days before the period" falls.
TSH. An underactive or overactive thyroid can upset cycles and ovulation. TSH is a simple first check of thyroid function.
Prolactin. High prolactin can stop ovulation or cause irregular periods, and sometimes a milky discharge from the nipples. Stress, a recent breast examination and some medicines can raise it temporarily, so a mildly high result is often repeated before anything else is done.
Good to know. Every laboratory uses its own methods and its own normal range. Always compare a result with the range printed on that report, not with a number from the internet or from another lab.
Other tests you may hear about
- AMH is a blood test for ovarian reserve that can be done on any day. It has its own limits: it reflects how many eggs remain, not their quality.
- Testosterone and related hormones may be checked if there are signs of PCOS, such as excess hair growth or acne.
- For the male partner, hormone tests such as FSH and testosterone are not usually the first step. They may be suggested if a semen analysis is unusual.
What hormone tests can't tell you
A single hormone result is a snapshot of one day. It does not measure egg quality, and it does not predict whether you will conceive in a particular month. Normal hormone results don't guarantee a pregnancy, and one result outside the range is not a diagnosis.
A doctor reads hormone tests together with your age, cycles, scan findings and your partner's results. If a result is unexpected, it is common to repeat it before drawing conclusions. Celova does not offer tests itself, but a doctor in an online consultation can go through reports you already have.
When to see a doctor
- Your periods are very irregular, have stopped, or come less often than every five weeks or so.
- You notice milky nipple discharge when you are not breastfeeding.
- You have symptoms of a thyroid problem, such as marked tiredness, weight change without a clear reason, feeling very hot or cold, or a racing heart.
- You have results you don't understand. Ask the doctor who requested them to explain what they mean for you; our appointment question builder can help you prepare.
Severe headaches with changes in your vision need prompt medical attention. For severe pain, heavy bleeding or fainting, call 112 or go to the nearest hospital.
Sources
This is general information, not medical advice. It can't account for your history. Please talk to a doctor about your own situation. Medical disclaimer
Severe pain, heavy bleeding or fainting? Call 112 or go to the nearest hospital.