Can I get pregnant if my thyroid is underactive?

Yes, but it is more difficult to conceive. There is also an increased risk of miscarriage.

Can I get pregnant if my thyroid is overactive?

Yes, but it is more difficult to conceive. If the overactivity is not treated there is an increased risk of miscarriage and premature delivery.

I’m hypothyroid. Should I continue to take my levothyroxine during my pregnancy?

Yes, as soon as you know you are pregnant it is usually recommended that your levothyroxine is increased immediately by 25-50mcg daily. You should then contact your GP and arrange to have a thyroid blood test

I’m hyperthyroid and take carbimazole. Is this okay during pregnancy?

For hyperthyroid (overactive) patients propylthiouracil (PTU) is the medication of choice during pregnancy for the first trimester only. Carbimazole is the drug used during the rest of pregnancy. 

You should discuss your plans for pregnancy with your endocrinologist before you try to conceive as it may be necessary to change your medication, or in some cases it can be stopped.

If you are being treated with antithyroid drugs (e.g. carbimazole or PTU) and you have not already discussed your pregnancy plans with them beforehand, you should contact your endocrinologist or GP as soon as possible after pregnancy is confirmed as it may be necessary to adjust your medication.

I have been treated with radioiodine for an overactive thyroid. Will this harm the baby?

You should not get pregnant for six months after this treatment. Men should avoid fathering a child for at least four months after this treatment. If you are in doubt check with your GP or specialist.

I have Graves’ disease treated by surgery and am taking levothyroxine. Are there any problems for the baby?

Firstly you should increase the dose of thyroxine during pregnancy. There is also a very small chance that the baby could be born with an overactive thyroid but if that happened it would only last for about one month and can be treated easily. A blood test during the later part of pregnancy will indicate if there is a high risk of this.

I was diagnosed with Graves’ disease a few years ago. After taking carbimazole for over a year I became euthyroid and was able to stop treatment. I am now trying to become pregnant and was wondering if I am now completely clear of hyperthyroidism or could the illness come back? 

You should have thyroid function tests and thyroid stimulating hormone receptor antibodies (TRAb) checked in the first trimester. Even if you are euthyroid, if the TRAb is positive, you should be referred to a local antenatal clinic during pregnancy. This is precautionary but because thyroid receptor antibodies cross the placenta, monitoring during pregnancy is recommended.

There is a risk of Graves' disease relapse pre-pregnancy or in early pregnancy, or the postpartum period. Thyroid function tests should be checked if you develop symptoms of hyperthyroidism at any stage, or in early pregnancy. 

Can I take antenatal vitamins if I have thyroid disease and take medication?

Yes, take your antenatal vitamins, but avoid taking them at the same time you take your thyroid medication. Some (e.g calcium and iron) interfere with the absorption of thyroid medication in your system.

I’ve heard that you can develop thyroid disease after you have a baby?

Up to 9% of women can develop postpartum thyroid disease. Sometimes this is a temporary condition. It can be treated with levothyroxine.  In some cases, the thyroid disease remains a permanent condition.

Can I breastfeed my baby if I am on levothyroxine or antithyroid medication?

Yes. Breastfeeding is safe while taking levothyroxine. Breastfeeding while taking antithyroid drugs is generally safe but you should check with your endocrinologist.


Subclinical hypothyroidism

I am just six weeks pregnant and haven’t been diagnosed with a thyroid disorder. But I’m worried as my TSH is raised above the normal reference range. Would it help me to start taking levothyroxine?

Current guidance is to start levothyroxine if the TSH is greater than the pregnancy-specific reference range, or greater than 4 mU/L if there are no pregnancy ranges available locally.

If TPO antibodies are raised then the current American Thyroid Association (ATA) guidelines would recommend treatment if the TSH is greater than 2.5 mU/L, however the benefit of treatment in this context is less clear.

I am trying to have a baby but sadly had two early miscarriages last year. I have a family history of thyroid problems and have tested positive for thyroid antibodies. Would taking levothyroxine improve my chances of having a successful pregnancy?

There is no evidence that treating women who have positive TPO antibodies but normal thyroid function tests will result in improved pregnancy outcomes even in those with previous pregnancy losses.

If the TSH is above the pregnancy-specific reference range (or greater than 4.0 mU/L where there are no pregnancy ranges available) then treatment with levothyroxine should be recommended.

The evidence for treating those with a TSH between 2.5 mU/Land the upper limit of the pregnancy reference range (or 4.0 mIU/L) who are TPO positive and have recurrent miscarriage is less clear and the TABLET trial showed no benefit. A number of fertility clinics and the current ATA guidelines however would treat someone with a TSH greater than 2.5 mU/L in this situation.

Further information for patients

Pregnancy and thyroid disorders - guidance for patients

BTF Guide to Pregnancy and fertility in thyroid disorders

2017 Guidelines of the American Thyroid Association for the Diagnosis and Management of Thyroid Disease during Pregnancy and the Postpartum

TABLET trial  (Thyroid AntiBodies and LevoThyroxine)

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