A doctors' group has revised its guidelines on thyroid treatments during and after pregnancy. The Endocrine Society produced the new guidelines. There are 52 of them, covering before, during and after pregnancy, as well as during breastfeeding. The guidelines say that women who are trying to get pregnant and have any history of thyroid problems should be tested for normal thyroid function. The society also said that pregnant women take prenatal vitamins containing 150 to 200 micrograms of iodine. And women who are breastfeeding should take 250 micrograms of iodine every day. These doses protect women and their babies from iodine deficiency. That can lead to an imbalance of thyroid hormone. This hormone is crucial for fetal brain development. The new guidelines update a 2007 version. They were published in the August issue of the Journal of Clinical Endocrinology and Metabolism.

By Howard Lewine, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

In most people with thyroid problems, diagnosis and treatment are straightforward. They are much more complicated in pregnant women.

Doctors have an excellent test to determine if a thyroid gland is functioning normally. Normal function means the gland is producing the right amount of thyroid hormone.

It’s a simple blood test that measures the level of thyroid stimulating hormone (TSH). The pituitary gland makes TSH and releases it into the blood. When TSH reaches the thyroid gland, it stimulates the gland to produce thyroid hormone.

In people with an underactive thyroid (hypothyroidism), the blood level of thyroid hormone drops below normal. If that happens, the pituitary gland releases more TSH. With rare exceptions, everyone with hypothyroidism has a high TSH level. The opposite is true if the thyroid makes too much thyroid hormone (hyperthyroidism). Then, the pituitary gland stops releasing TSH. The blood level of TSH gets very low.

Doctors also use TSH level to find out if a patient with hypothyroidism is taking the right dose of thyroid pills.

Experts don't always agree on the normal range for TSH, even for non-pregnant women. The reports from most laboratories show a normal range of 0.45 to 4.5 milli-international units per liter of blood (mIU/L). However, many thyroid experts use a normal range to 0.3 to 3.0 mIU/L. Pregnancy complicates the diagnosis and treatment of thyroid problems. And not just a little. This month the Endocrine Society published 52 separate recommendations to help doctors with this task. The guidelines provide information before, during and right after pregnancy. They also give information for breastfeeding moms. Why are there so many recommendations for something that most doctors consider rather straightforward? We still have a lot to learn about the fine points related to thyroid problems and pregnancy, and expert opinion varies. Don’t let this scare you. These fine points are not what is important in helping you have a successful pregnancy and a delivering a healthy baby. By taking some preventive measures, paying attention to your body and working closely with your health care team, thyroid problems will most often be "no problem."

What Changes Can I Make Now?

Here are the major takeaways from the guidelines:

• Any woman with a history of a thyroid disorder should have a blood test for TSH if she is trying to become pregnant. Even a mildly elevated TSH may indicate a need for thyroid pills. Regulating a thyroid disorder can improve fertility.



• Women considering pregnancy should make sure they get an average of 250 micrograms of dietary iodine daily. If dietary sources don't provide enough iodine, take a multivitamin with 150-200 micrograms of iodine. But don’t overdo it: More is not better.



• Pregnant women should take a daily prenatal vitamin containing 150-200 micrograms of iodine.



• Women with any history of a thyroid disorder should definitely have a TSH within the first 9 weeks of pregnancy. Some experts recommend routine TSH testing for all pregnant women.



• Women with hypothyroidism will usually need a higher dose of thyroid replacement once they become pregnant. The goal TSH level is generally less than 2.5 mIU/L. This is lower than the goal level in men and non-pregnant women.



• Women taking medication for an overactive thyroid (hyperthyroidism) need to carefully review their medicines once they are pregnant. The drugs recommended may be different than what they took prior to pregnancy.



• Women who are breastfeeding should maintain an average daily intake of 250 micrograms of iodine.

What Can I Expect Looking to the Future?

Guidelines help you and your doctor consider the options that are best for you. But they do not dictate what must be done for everyone. Similar to all guidelines, these recommendations provide the most current evidence to help prevent, diagnose and treat a specific condition.