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HealthInfo Canterbury

Thyroid disease in pregnancy

If you have an overactive thyroid (hyperthyroidism) or underactive thyroid (hypothyroidism), you'll need some extra care and monitoring while you're pregnant to keep you and your baby well.

Overactive thyroid

You have a normal chance of becoming pregnant as long as your overactive thyroid is controlled.

It's best not to become pregnant while you're being treated for an overactive thyroid. The medicines can harm a baby's thyroid gland.

But if you get pregnant, it's important to keep taking your medicine. Your GP will arrange for you to see a specialist, who'll work out what dose of medicine will control your overactive thyroid while reducing the risk to your baby.

After you've finished treatment, you'll have a normal chance of becoming pregnant.

You'll need to have regular thyroid blood tests while you're pregnant.

Unlike other women, you won't need to take iodine supplements while pregnant because they could make your overactive thyroid worse.

You can't have a nuclear medicine scan or radioiodine treatment while you're pregnant, as they aren't safe for your baby.

Underactive thyroid

If you have an underactive thyroid (hypothyroidism), you'll need regular blood tests when planning a pregnancy and through your pregnancy.

It's important that you have the right dose of thyroxine for both you and your baby. If you don't have enough thyroxine, you could have problems such as anaemia (not enough red blood cells), heart failure, problems with the placenta or bleeding after delivery.

Most women need to take a higher dose of thyroxine while they're pregnant then go back to their normal dose once their baby is born.

Written by HealthInfo clinical advisers. Endorsed by midwife liaison, Canterbury DHB. Last reviewed October 2019. Last updated May 2020.

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Thyroid

Page reference: 435549

Review key: HIHCP-311277