Thyroid problems in pregnancy: tests, medicine and what to do

If you have thyroid problems in pregnancy, your main job is keeping your levels steady with your doctor's help. Tell your gynae as soon as you know you're pregnant and keep taking any thyroid medicine. You'll have more blood tests than usual. Changi General Hospital (CGH) says that with the right treatment and regular checks, women with Graves' disease can have healthy pregnancies and smooth deliveries.

What to do about thyroid problems in pregnancy, step by step

1. Tell your gynae and your thyroid doctor as soon as you know you're pregnant. The NHS says you'll need more tests, and your levothyroxine dose is likely to change.
2. Keep taking your thyroid medicine until you've spoken to your doctor. HealthHub says not to stop levothyroxine, or switch brands, without telling your doctor.
3. Leave dose changes to your doctor. CGH says women on thyroid hormone need a higher dose in pregnancy, with closer checks.
4. Go for every thyroid blood test you're booked for. CGH says your care team monitors your thyroid closely throughout pregnancy and adjusts your medicine as it goes.
5. Keep your thyroid tablet apart from iron and calcium. CGH says to take levothyroxine at least four hours apart from calcium and iron supplements, so ask your pharmacist how to fit it around your prenatal vitamins.
6. Ask your doctor which medicine suits early pregnancy if you have Graves' disease, and let them make any change. CGH says propylthiouracil (PTU) is recommended then, as it carries a lower risk of birth defects than carbimazole.
7. Ask for a thyroid test if you've had thyroid trouble before or have symptoms. It isn't one of the six routine blood tests HealthHub lists for every mum-to-be.
8. Plan a thyroid check after the birth. CGH says Graves' disease tends to improve late in pregnancy but can worsen or come back after delivery.
9. Carry on breastfeeding if you'd like to. CGH says it's generally safe on anti-thyroid medicine and suggests taking your tablet after a feed.

Why your thyroid needs closer care in pregnancy

Your thyroid is the butterfly-shaped gland at the front of your neck, and CGH says its hormones help control your metabolism, temperature, heart rate and weight. Pregnancy hormones shift your thyroid levels naturally. That's why your doctor reads each thyroid result against your stage of pregnancy.

Good control protects your baby. The NHS says an untreated underactive thyroid raises the chance of pre-eclampsia, premature birth or miscarriage, and that treatment usually helps prevent these. For an overactive thyroid that isn't well controlled, CGH lists pre-eclampsia, miscarriage, restricted growth for the baby and early delivery.

Graves' disease adds one more thing to watch. CGH explains that thyroid antibodies, even from Graves' you had in the past, can stimulate your baby's thyroid. So your care team rechecks antibodies during pregnancy, and your obstetrician checks the baby's thyroid on regular scans.

Underactive, overactive or postpartum thyroiditis: how they differ

The signs below are reasons to get a blood test, not a diagnosis. The NHS says a thyroid check measures two things in your blood: thyroid-stimulating hormone (TSH) and thyroxine (T4).

Thyroid tests in pregnancy in Singapore

A thyroid test isn't on the routine list. HealthHub names six blood tests every mum-to-be has: a full blood count, blood typing, screening for hepatitis B, syphilis and HIV, and the glucose test for gestational diabetes. So you or your doctor has to ask for it.

Bring it up at your first gynae visit if you've had thyroid treatment, surgery or radioactive iodine, or if you have symptoms. The NHS says a doctor checking your thyroid will also ask whether thyroid or autoimmune conditions run in your family. Our check-up and scan schedule shows when the routine tests happen.

Planning a pregnancy? CGH asks women who have or had Graves' disease, or who've had radioactive iodine or thyroid surgery, to tell their doctor at least six months ahead. That gives time to bring your levels into range first. Our trying to conceive guide covers the pre-pregnancy check.

Medicines and breastfeeding

CGH says medicine is the main treatment for Graves' disease in pregnancy. A heart-rate medicine may be used for a short time to ease palpitations or shaky hands. Radioactive iodine is unsafe in pregnancy, and surgery is kept for rare cases, usually in the second trimester.

Check every other medicine and supplement first; our guide to safe medicine during pregnancy shows how. HealthHub asks you to tell your doctor or pharmacist about vitamins such as calcium, herbal products and traditional remedies, because some of them change your levothyroxine level.

After the birth, CGH says breastfeeding is generally safe on anti-thyroid medicine, because only small amounts pass into breast milk. Our page on medicine while breastfeeding covers other medicines.

After the birth: postpartum thyroiditis

Your thyroid can change again once your baby arrives. Cleveland Clinic says postpartum thyroiditis affects about 5% to 10% of women in the year after a birth, miscarriage or abortion. It often starts with an overactive phase one to six months after, then an underactive phase four to eight months after. Then the thyroid usually returns to normal.

Cleveland Clinic says most people don't notice symptoms until the underactive phase. Tiredness, low mood and weight gain are easy to blame on a new baby. You're more likely to get it if you've had it before, have type 1 diabetes, or have a personal or family history of thyroid disease. A blood test usually confirms it, and most women with mild symptoms need no treatment.

Mention any of this at your six-week postnatal check. If hair shedding is what you've noticed, our guide to postpartum hair loss explains when to ask for a thyroid test.

When to see a doctor

Call your gynae's clinic or see a GP if you notice any of these.

• A racing or irregular heartbeat, chest pain or shortness of breath. HealthHub's levothyroxine page says to get medical advice right away for these, and CGH names palpitations as a symptom it treats in pregnancy.
• Vomiting that won't settle, or losing weight. KKH's Urgent O&G Centre lists vomiting in pregnancy among the problems it sees, and our morning sickness guide explains hyperemesis.
• A new lump or swelling in your neck. The NHS says a GP may examine your neck to see if your thyroid is swollen.
• Shaky hands, anxiety or weight loss without trying, in pregnancy or the months after. CGH lists hand tremors, and Cleveland Clinic lists anxiety and weight loss in the overactive phase after birth.
• Low mood, exhaustion or weight gain in the year after birth. Cleveland Clinic lists these in the underactive phase of postpartum thyroiditis. Low mood can also be postnatal depression, so read our postnatal depression guide too.
• A fit or seizure. HealthHub's levothyroxine page lists seizures among the effects that need medical help right away, and KKH says to call 995 for emergencies.

Where to go: before 22 weeks, or for a problem after the birth, KKH's Urgent O&G Centre is a 24-hour walk-in centre at Basement 1 of Women's Tower. At 22 weeks or more, KKH asks you to go straight to its Delivery Suite on Level 2 of Women's Tower. For an emergency, KKH says to call 995 or go to an emergency room. Our guide to bleeding in early pregnancy lists the urgent routes at other hospitals.

Frequently asked questions

Is hypothyroidism in pregnancy dangerous for the baby?

Untreated, it can be. The NHS links an untreated underactive thyroid with pre-eclampsia, premature birth and miscarriage, and says treatment usually helps prevent these. Keep taking your levothyroxine, and let your doctor raise the dose as CGH describes.

Can you have a normal pregnancy with hyperthyroidism?

Yes, with treatment and regular checks. CGH says women with Graves' disease can have healthy pregnancies and smooth deliveries. Expect regular blood tests and scans that check your baby's thyroid. Your doctor may move you onto PTU in early pregnancy.

Is a thyroid test done in pregnancy in Singapore?

Not as one of the routine tests. HealthHub's list of six routine blood tests for every mum-to-be doesn't include one. Your gynae can order TSH and T4 if you have symptoms or a thyroid history, so ask at your first visit.

Should I stop my thyroid medicine when I find out I'm pregnant?

No. Keep taking it and call your doctor. HealthHub says not to stop levothyroxine without checking with your doctor, and CGH says the dose needs to go up in pregnancy. If you take carbimazole, call your doctor straight away, as CGH says PTU is recommended in early pregnancy.

Do thyroid problems in pregnancy go away after birth?

They can change. CGH says Graves' disease tends to improve late in pregnancy but can worsen or come back after delivery. Postpartum thyroiditis can also start in the year after birth, and Cleveland Clinic says the thyroid usually returns to normal. Either way, get your levels checked after the birth.