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Thyroid Diseases

I Have Grave Disease But Want to Get Pregnant

03/02/2009

Question:

Hi, I was diagnosed with Grave’s disease last summer of 2008. I have been taking methimazole to control my hormones and propranolol for the heart rate for one month now. My doctor told me that if I wanted to concieve (get pregnant) than I will have to stop taking methimazole for about a month. Then I can conceive. I want to know is that true. My doctor also mentions RAI but I feel that it safe to take it because I can become hypo. If I did get pregnant is there any risk for me or my child. What medication is safe to take when I am pregnant? Any information I should know before even getting pregnant. Thank you

Answer:

I don't think your doctor meant that you should stop taking methimazole for a month and then try to get pregnant without taking any anti-thyroid drugs at all. Generally we try to use propylthiouracil (PTU) instead of methimazole in patients who are trying to get pregnant, though the evidence that this is necessary is not overwhelming. There is some evidence that methimazole crosses the placenta (and gets into breast milk too) a little easier than PTU. Also, birth defects (which are rare no matter which drug is used) have been reported a little more with methimazole than with PTU.

On the other hand, problems from methimazole in pregnancy seem to be pretty rare. It has been recommended that pregnant patients who are allergic to PTU be tried on methimazole rather than attempting treatment with surgery.

Radioactive iodine is, of course, not given to patients who are known to be pregnant. If you wanted to be treated with radioactive iodine it would generally be considered smart for you to avoid pregnancy for 6 months after the treatment. The radioactive iodine would make your thyroid levels go low after about 3 months, but then you would be started on a thyroid hormone pill and this would return your thyroid blood tests to normal after a few months.

In conclusion, the recommendation that you switch from methimazole to PTU is a reasonable one, though things would most likely turn out all right if for some reason you insisted on staying on methimazole before and during your pregnancy. Regardless of whether you used radioactive iodine or PTU, it would be best for your thyroid blood tests to be completely normal before you tried to get pregnant.

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Response by:

Thomas A Murphy, MD, FACP, FACE Thomas A Murphy, MD, FACP, FACE
Associate Professor of Medicine
School of Medicine
Case Western Reserve University