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Hyperthyroidism in pregnancy

Dr Roger Henderson
Reviewed by Roger HendersonReviewed on 29.04.2024 | 3 minutes read

Having an overactive thyroid gland, or hyperthyroidism, during pregnancy requires close monitoring under specialist supervision. There’s no reason you shouldn’t expect a healthy you, a healthy baby and a normal delivery. It’s best to seek help early – ideally before you conceive – and keep up with recommended blood tests and medication changes throughout and after pregnancy.

What are the risks in pregnancy?

Unfortunately, if thyroid function is not kept under tight control, it carries risks to you and your baby, including miscarriage, pre-eclampsia, preterm birth (before 37 weeks) and low birth weight. There's also a very small chance in the case of Grave's disease of antibodies crossing the placenta and affecting the baby's thyroid gland. You will have your antibody levels at a certain point during your pregnancy, and all babies are screened for thyroid disease at birth.

You also need to seek urgent medical attention if you experience a very fast heart rate, high blood pressure and high body temperature, as on rare occasions, pregnancy can cause a thyroid storm, where thyroxine levels soar to very high levels. This needs immediate treatment.

Rest assured, hyperthyroidism is common, affecting around 2 in every 1000 pregnancies, so there’s lots of research, and doctors are skilled at treating it.

Should I do anything before getting pregnant?

The earlier you seek advice, the better, so discuss your plans to become pregnant ahead of time with your endocrinologist. From the outset, good control of thyroid function is essential for fertility in both men and women.

If you are on medication to block thyroid hormones, they may suggest a permanent solution: surgery to remove some or all of the thyroid gland is usually the preferred option. Radiotherapy (radioiodine treatment) is another option, but you will have to delay conception for at least six months afterwards.

After surgery or radiotherapy, you may have to take thyroxine replacement tablets, so you need a few months to establish the right levels on this. The levothyroxine dose will be increased during pregnancy, as requirements always rise.

If it’s decided best to remain on thyroid-blocking medication, your endocrinologist may change this to one that is safer in pregnancy. This is safe to continue in breastfeeding, too.

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Does pregnancy make thyroid function worse or better?

Good question, and as with most answers related to pregnancy, it’s difficult to tell which way it will go for each individual. Some find control of thyroid function worsens in the first trimester, and others find they have better control overall. If you are taking levothyroxine as a replacement after surgery, this dose will be increased at the start of pregnancy, as requirements rise for all women who are effectively hypothyroid.

Most women return to pre-pregnancy thyroid function after birth – you should have your thyroid function checked around six weeks after delivery and medications may be adjusted then.

How can I help myself?

All women should take folic acid and vitamin D supplements when thinking about becoming pregnant and for the first three months of pregnancy. To ensure optimum health of your growing baby, it's recommended that every woman stops smoking, if applicable, and limits alcohol. You should keep hydrated, especially as pregnancy increases requirements, and follow a diet full of fresh fruit and vegetables, whole grains and fibre. Maintaining gentle activity levels, as able, and making sure you are getting enough rest and relaxation time will help all body systems while your body changes and adapts.

All of this will help you stay healthy and in tune with your body, so you can be more alert if symptoms creep in.

Unfortunately, there is nothing specific that you can do to control your thyroid function, except make sure you don’t miss out medications and keep up with all your thyroid function tests. If vomiting is persistent or prolonged, you should discuss this with your specialist, as medication may not have a chance to be absorbed into your system.

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Dr Roger Henderson
Reviewed by Roger Henderson
Reviewed on 29.04.2024
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