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Thyroid Disorders Again Linked to Birth Defects

Mother's under-active thyroid increases risk of heart, kidney and brain damage, study says

THURSDAY, Jan. 17, 2002 (HealthDayNews) -- For the second time this week, a new study has linked low thyroid function to birth defects.

In the latest research, doctors at Johns Hopkins Medical Center offer what they say is proof that babies born to women with abnormally functioning thyroid glands are at increased risk for heart, kidney and brain damage, as well as other more common defects such as cleft lip and palate.

"By far, the greatest number of birth defects seen involved the heart. Although there were other problems as well, including renal and central nervous system problems, limb defects such as cleft foot, as well as cleft palate, all of which were seen in greater numbers in women who had a low thyroid function," says study author Dr. David A. Nagey. He presented his findings today at the annual meeting of the Society for Maternal-Fetal Medicine in New Orleans.

All of these defects were seen, even though the women were on medication to offset the problems created by abnormally functioning thyroids.

Although women with both low (under-active) and high (over-active) thyroid functions had increased risks of birth defects, Nagey says the babies of women with under-active thyroids fared the worst, particularly when it came to heart abnormalities.

In the past, studies have shown that babies born to mothers with under-active thyroids can have developmental problems, including learning disabilities. Some studies have also shown a slight increase in the risk of Down's syndrome.

But the Hopkins study is the first human study to indicate that thyroid function may also be linked to physical birth defects.

However, endocrinologist and thyroid expert Dr. Loren Wissner-Greene has some doubts about the study's conclusions.

"Women with thyroid disorder have been studied and studied extensively. And even in a very large trial published last year in The New England Journal of Medicine, babies born to mothers with thyroid disease were, at most, found to have slight developmental delays. There was never any mention of any possibility of these kinds of major birth defects," says Wissner-Greene, associate professor of medicine at New York University Medical Center.

"One would think that if the results were as obvious as they seem in this study, there would have been some indication noted long before this. And this hasn't been so," says Wissner-Greene, who questions whether some other unknown factor could have been responsible for the finding.

Earlier this week, researchers at Texas A& M University reported that a study of sheep found alcohol-related birth defects, which include some physical deformities, may be linked to thyroid function.

"We found that the thyroid gland is suppressed by the alcohol, which, in turn, may be the underlying cause of alcohol-related birth defects," says Dr. Timothy Cudd, associate professor of physiology at Texas A&M and author of the earlier study.

Nagey of Hopkins says he's not certain how or why an under-active thyroid increases the risk of birth defects. But he suspects the same underlying problem that causes the thyroid gland to malfunction -- an autoimmune response -- may be to blame for the birth defects.

His study involved 101 pregnant women all previously diagnosed with thyroid disorder -- 64 with low thyroid function and 50 with high thyroid function. All gave birth at Johns Hopkins Hospital between 1994 and 1999. The average age of each mother was 31, and Nagey says very few admitted to drinking alcohol, smoking, or using drugs.

After studying the medical charts on all the women and the 114 babies who were born, the doctors noted a higher-than-average rate of numerous birth defects.

Twenty one babies (18 percent) had birth defects, ranging from cardiac, renal and central nervous system problems, to deformities such as sunken chest, extra fingers, cleft lip and palate and ear deformities. Two other babies died before being delivered.

For Nagey, the true value of his research is in underscoring the need for high-risk obstetrical care for women with a thyroid disorder.

"I think our study verifies once again that women with a thyroid disorder require the care of a high-risk obstetrician," says Nagey.

More important, he says, is the need to choose a birthing center that is experienced in the post-natal care of babies with the types of birth defects seen in this study.

"The hospital needs to be equipped to handle the kind of problems we found in this study, to do whatever immediate surgery or other treatments are necessary as soon as the baby is born," says Nagey.

Wissner-Greene cautions, however, that women should not panic over the Hopkins research. The study contained a small number of women and the results are controversial, she says.

"Even if the finding is validated in larger studies, it should be noted that not every woman with a thyroid disorder is going to give birth to a defected baby. And the research, even if proven true, will only pertain to a relatively small number of women," she adds.

What To Do:

For more information on thyroid disorders, visit the American Thyroid Society.

For an overview of how the thyroid gland works and how it can affect your health, visit The Thyroid Society.

To learn more about how thyroid disorders affect pregnancy, check this Colorado State University site.

SOURCES: Interviews with David A. Nagey, M.D., Ph.D., study author, associate professor of obstetrics and gynecology, Johns Hopkins Medical Center, Baltimore; Timothy A. Cudd, D.V.M., Ph.D., associate professor of physiology, Texas A&M University, College Station; Loren Wissner-Greene, M.D., associate professor of medicine, New York University School of Medicine, New York City; study presentation Jan. 17, 2002, Society for Maternal-Fetal Medicine annual meeting, New Orleans
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