Thyroid Treatment Guidelines for Pregnant Women Revised

Christina Bates -

Thyroid hormone is critical for normal fetal brain development, and hormonal problems among pregnant women must be properly managed, according to the Endocrine Society, which has recently revised its guidelines on treating thyroid-related medical issues before, during and after pregnancy.

Too much or not enough thyroid hormone can harm both women and their unborn babies, the experts said. The recent treatment guidelines update the 2007 version.

"Pregnancy may affect the course of thyroid diseases and, conversely, thyroid diseases may affect the course of pregnancy," said lead study author Leslie de Groot, MD, a research professor at the University of Rhode Island, in a society news release. "Pregnant women may be under the care of multiple health care professionals, including obstetricians, nurse midwives, family practitioners and endocrinologists, making the development of guidelines all the more critical."

Women who are hypothyroid (underactive thyroid function) are at greater risk for infertility and are more likely to have anemia, gestational hypertension and postpartum hemorrhage, the news release noted. If not treated, hypothyroidism during pregnancy can lead to premature birth, low birth weight and respiratory distress among newborns. Overactive thyroid function, or hyperthyroidism, also can lead to miscarriage.

The Endocrine Society made the following revisions to its clinical practice guidelines:

  • Doctors should interpret serum-free thyroxine levels cautiously during pregnancy. The experts advised that using trimester-specific reference ranges would improve the interpretation of pregnant women's thyroid-function tests.
  • The drug propylthiouracil (PTU) should be the primary treatment for hyperthyroidism during the first trimester of pregnancy. The experts cautioned the alternate treatment-methimazole-may increase the risk for birth defects. Methimazole, however, can be used if PTU is unavailable or if women have a negative reaction to the drug. Because PTU may be harmful to the liver in rare cases, once women complete their first trimester, they should switch from PTU to methimazole.
  • Women who are breast-feeding should take 250 micrograms of iodine daily to ensure their infants are getting 100 micrograms of iodine each day.
  • Daily prenatal vitamins should contain 150 to 200 micrograms of iodine to protect women from iodine deficiency.
  • Women with Graves' disease, a history of Graves' disease, a previous newborn with Graves' disease or previously elevated thyroid stimulating hormone antibodies should have these antibodies measured before they are 22 weeks pregnant. These antibodies cross the placenta and can stimulate or restrict the fetal thyroid, the experts explained.
  • The fetuses of women who have thyroid stimulating hormone receptor antibodies at least two to three times higher than normal or who are treated with anti-thyroid drugs should be screened for thyroid problems. This can be done during the fetal ultrasound women routinely undergo when they are between 18 and 22 weeks pregnant. An enlarged thyroid, growth restriction, severe swelling, presence of goiter, advanced bone age or heart failure could be signs of thyroid problems in a fetus.
  • Fine-needle aspiration should be considered for women with nodules 5 millimeters to 1 centimeter in size who have a high-risk history or suspicious findings on an ultrasound. Women with complex nodules 15 centimeters to 2 centimeters also should undergo this procedure. The guidelines note that this can be delayed until after delivery for women who are at least 34 weeks pregnant.

The news release noted that consensus was not reached on whether all newly pregnant women should be screened for thyroid problems, but added that some experts support universal screening for thyroid problems by the time women are nine weeks pregnant.

The revised guidelines appear in the Journal of Clinical Endocrinology and Metabolism.