Approximately one out of every 100 pregnant women will have a thyroid problem during pregnancy. The thyroid may be come underactive during pregnancy (hypothyroidism) or overactive (hyperthyroidism). In about 10% to 15% of pregnant women, there is evidence of an autoimmune thyroid disorder that may not yet be affecting thyroid function. Sometimes a nodule in the thyroid is found, and rarely, this may be a thyroid cancer. These issues are not usually cause for alarm for mother or baby, but treatment may be needed for a successful pregnancy.
Hypothyroidism During Pregnancy
Uncontrolled hypothyroidism in pregnancy can cause lower IQ in the baby. Women who are found to have an underactive thyroid should be treated with thyroid hormone and stabilized as soon as possible, particularly in the first trimester. Levothyroxine (T4) is used to replace thyroid hormone and is safe to use during pregnancy. Thyroid levels will need to be checked every four to six weeks during the pregnancy to insure thyroid medication is appropriate.
Women with hypothyroidism who want to become pregnant should work with their healthcare providers to make sure their thyroid medication is appropriate. The TSH level should be less than 2.5 mIU/ml before pregnancy for optimum health of the baby and mother. Hypothyroid women should notify their practitioner as soon as they discover their pregnancy. Most patients will need in increase in their levothyroxine dose during the pregnancy in order to maintain proper thyroid levels.
Hyperthyroidism During Pregnancy
Subclinical hyperthyroidism is common during the first trimester of pregnancy and does not usually require treatment. This occurs when pregnancy hormone levels cause the TSH to decrease, though the free T4 and free T3 levels usually remain relatively normal. Excessive nausea due to morning sickness or hyperemesis gravidarum can also cause the TSH level to be low. Women are monitored by checking thyroid levels every four to five weeks. Treatment is not necessary while free T4 and free T3 levels remain normal. The thyroid levels will usually improve on their own in the second or third trimester.
Graves' disease does require treatment during pregnancy to help protect both mother and baby. Untreated hyperthyroidism can lead to problems in the baby, including:
- low birth weight
- enlarged thyroid
- heart failure
Treatment of hyperthyroidism during pregnancy is usually with a thyroid-blocking medication known as PTU (propylthiouracil). Thyroid labs will need to be monitored every four to six weeks. Graves' antibody blood tests should also be checked since these antibodies may cross the placenta. Levels should be drawn in the first and last trimesters. The baby will need to be monitored at birth for signs of hyperthyroidism that can be caused by the mother's thyroid antibodies.
Outcomes for Thyroid Dysfunction During Pregnancy
Most women and their babies do very well with thyroid problems during pregnancy. It's important for a woman to have appropriate prenatal care to identify any thyroid issues early for proper treatment. Someone with a thyroid disorder who becomes pregnancy should notify their healthcare provider immediately in case any changes in their treatment are needed.
Source:
The Endocrine Society's Clinical Guidelines. Management of Thyroid Dysfunction During Pregnancy and Postpartum
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