Thyroid problems and high prolactin can both disturb periods and ovulation. They are checked with simple blood tests, and both are usually treatable. Medicines should only be started, changed or stopped with a doctor.
Why these hormones matter
Ovulation depends on a chain of signals between the brain, the pituitary gland (a small gland at the base of the brain) and the ovaries. The thyroid gland and the hormone prolactin can both interfere with these signals. When they are out of balance, periods may become irregular or stop, and ovulation may not happen.
The good news is that both are usually straightforward to test, and both are usually treatable.
The thyroid
The thyroid is a gland in the neck that makes hormones controlling the body's energy use.
- Underactive thyroid (hypothyroidism) can cause tiredness, weight gain, feeling cold, constipation, dry skin, and heavy or irregular periods. It may affect ovulation.
- Overactive thyroid (hyperthyroidism) can cause weight loss, a fast heartbeat, anxiety, shakiness, feeling hot, and light or infrequent periods.
Thyroid conditions are common in women, and having a family history raises the chance. An underactive thyroid can also raise prolactin levels, which is one reason the two are often checked together.
Thyroid health also matters during pregnancy, because the developing baby relies on the mother's thyroid hormones in the early weeks.
Prolactin
Prolactin is a hormone made by the pituitary gland. Its main job is to support breast milk production. Outside breastfeeding, high levels (hyperprolactinaemia) can switch off ovulation.
Possible signs include:
- irregular or absent periods
- a milky discharge from the nipples when not breastfeeding
- in some cases, headaches or changes in vision
Common causes include some medicines (including certain medicines for mental health and for nausea), an underactive thyroid, and a small, non-cancerous growth on the pituitary gland called a prolactinoma. Prolactin can also rise briefly with stress, exercise or a difficult blood draw.
In men, high prolactin can lower testosterone and cause low sex drive or erection problems. A male partner with these symptoms should mention them to a doctor; our guide to causes of male infertility explains what else is checked.
The tests
| Test | What it checks | Notes |
|---|---|---|
| TSH (thyroid-stimulating hormone) | The main screening test for thyroid function | Usually the first test |
| Free T4 | The level of thyroid hormone in the blood | Often done if TSH is unusual |
| Thyroid antibodies (TPO) | Whether the immune system is affecting the thyroid | Sometimes checked, for example after recurrent pregnancy loss |
| Prolactin | The level of prolactin | A raised result is often repeated before further tests |
Laboratories use different reference ranges, so use the range printed on your own report and ask a doctor to interpret it. A mildly unusual result does not always need treatment; it depends on symptoms, your history and repeat results. Our guide to hormone blood tests for fertility covers the other tests often done at the same time.
If prolactin stays high, a doctor may check for macroprolactin (a form of prolactin that usually causes no problems) or suggest an MRI scan of the pituitary gland.
Good to know. Testing thyroid and prolactin is usually only suggested when there are symptoms or irregular periods, or for specific reasons. Not everyone needs these tests as routine.
Treatment
- Underactive thyroid is usually treated with daily thyroid hormone tablets, with blood tests to adjust the dose.
- Overactive thyroid has several treatment options. Some are not suitable during pregnancy or while trying, so planning matters.
- High prolactin is usually treated with medicines that lower it, and periods and ovulation often return. If a medicine you take is the cause, your doctor may review it.
If you take thyroid medicine and become pregnant, tell your doctor promptly, because the dose often needs adjusting early in pregnancy.
Caution. Don't start, stop or change thyroid or prolactin medicines on your own, or take tablets someone else was prescribed. Never stop a mental-health medicine suddenly because you read it can raise prolactin; talk to the doctor who prescribed it first.
When to see a doctor
- Your periods are irregular, very light, very heavy or have stopped.
- You notice milky nipple discharge when not breastfeeding.
- You have symptoms of an under- or overactive thyroid.
- You take thyroid medicine and are planning a pregnancy, or have just found out you are pregnant.
New severe headaches with sudden changes in vision need urgent care: 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.