Thyroid Disease Increases Birth Defects

Jan. 18, 2002 -- Women with thyroid disease are more likely to have a child with birth defects -- even if thyroid tests taken during pregnancy are normal. A researcher at the Society for Maternal-Fetal Medicine meeting in New Orleans is recommending testing before getting pregnant.

Babies born to women with thyroid disease are at increased risk of heart, brain, and kidney defects, says lead author David Nagey, MD, PhD, in a news release. Nagey is associate professor of gynecology and obstetrics at Johns Hopkins Medical School.

The infants are also at risk for physical abnormalities like cleft lip or palate or extra fingers, he reports.

The risk for heart defects was seen in women with an underactive thyroid but not in women with an overactive thyroid. And this was true even if the women were taking medication to bring their thyroid levels back to normal.

"We already knew that there was an increased risk of problems, mostly intellectual or developmental ... but the link with birth defects is new and unexpected," Nagey says.

If the study results are confirmed, it could lead to routine testing of women for thyroid disease prior to pregnancy. If the test indicates a woman has an underactive thyroid, a fetal ultrasound of the heart -- called an "echocardiogram" -- during the 20th week of pregnancy might be necessary, he says.

Nagey's study involved 64 women with underactive thyroid (known as hypothyroidism) and 50 with overactive thyroid (hyperthyroidism) who gave birth at Johns Hopkins between December 1994 and June 1999. Their average age was 31; very few admitted to smoking, drinking alcohol, or using illegal drugs during their pregnancy, he reports.

Overall, there were 108 pregnancies with 114 fetuses.

Twenty-one babies (18%) had birth defects, including problems in the heart, kidneys, and central nervous systems. They also had disorders like sunken chest, extra fingers, cleft lip and palate, and ear deformities. Two died before birth.

Hypothyroidism caused more birth defects than did hyperthyroidism. It's possible that the same antibodies that cause the underactive thyroid also could be responsible for the birth defects, Nagey says.

He recommends that women discuss thyroid testing with their doctor before getting pregnant.

But this study contradicts findings from earlier research that showed no increased risk of birth defects in women with thyroid disease that was under control. But Nagey says that those studies were done with less sophisticated technology.