Results of the study, to be presented Jan. 17 at the annual meeting of the Society for Maternal-Fetal Medicine in New Orleans, showed that babies born to women with overactive or underactive thyroid also were at increased risk of a variety of other anomalies, including cleft lip or palate, or extra fingers. In addition, infants born to women with underactive thyroid were at increased risk of cardiac problems even if the mothers were on medication.
The research contradicts some earlier studies indicating thyroid disease did not pose fetal risks, but those studies were conducted using less sophisticated technology for detecting birth defects, says David A. Nagey, M.D., Ph.D., study co-author and associate professor of gynecology and obstetrics.
"We already knew that there was an increased risk of problems, mostly intellectual or developmental, in children as a result of hypothyroid (underactive thyroid) pregnancies, but the link with birth defects is new and unexpected," Nagey says. "If these results are confirmed, it could lead to routine testing of women for thyroid disease prior to pregnancy and for cardiac anomalies in the fetuses of women with hypothyroidism."
Nagey recommends that doctors consider thyroid testing during a woman's pre-pregnancy consult or add it to the routine prenatal diagnostic tests. If the test indicates the woman has hypothyroidism, a fetal echocardiogram during the 20th week of pregnancy might be warranted.
The researchers studied 101 women (64 with hypothyroidism and 50 with the overactive version, hyperthyroidism) who gave birth at The Johns Hopkins Hospital between December 1994 and June 1999. The women's average age was 31; very few admitted to smoking, drinking alcohol or using illegal drugs. Overall, there were 108 pregnancies with 114 fetuses. The research team studied the charts for all children born from these pregnancies and recorded any medical problems during the neonatal period or subsequent years.
Twenty-one babies (18 percent) had birth defects, including problems in the cardiac, renal and central nervous systems and other disorders such as sunken chest, extra fingers, cleft lip and palate, and ear deformities. Two fetuses died before being delivered.
Among a subset of 86 women who had a test of their thyroid function performed during the first trimester of pregnancy (52 with hypothyroidism and 34 with hyperthyroidism), 17 babies (20 percent) had medical problems similar to those seen among the larger group.
The women with hypothyroidism were more likely than those with hyperthyroidism to have babies with defects. Nagey says it's possible the same antibodies that cause the underactive thyroid also could be responsible for the birth defects.
Adam J. Wolfberg, M.D., M.P.H., of Brigham and Women's Hospital, Boston, was principal author of the study. He was a medical student at Hopkins when the research was conducted.
Abstract # 274: Wolfberg, Adam J. and David A. Nagey, "Thyroid Disease During Pregnancy and Subsequent Congenital Anomalies."
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