Debate over who needs a thyroid check in pregnancy

Check-ups during pregnancy tend to focus around the waist. But there's growing debate about which mothers-to-be should have a gland in their neck tested, too.

Numerous studies since 1999 have found that an underactive thyroid can raise a woman's risk of miscarriage, premature birth, or a lower IQ for her baby — even if it's so mildly sluggish that she feels no symptoms.

The problem: While serious cases are treated with a hormone pill, so far there's little evidence that treating the milder cases makes a difference. So guidelines about who should be tested vary widely.

Now a peek at prenatal testing from one of the country's largest medical labs suggests that nearly a quarter of pregnant women are getting the simple thyroid blood test regardless of whether they have symptoms.

Researchers at Quest Diagnostics examined records for half a million pregnant women. Of those who got tested, a higher-than-expected number — 15 percent — had an underactive thyroid. That's five-fold higher than some previous estimates, partly because the way in which the condition is diagnosed has changed recently, says the study published by the Journal of Clinical Endocrinology & Metabolism.

The vast majority of those women were in the gray zone, with milder cases where no one knows for sure if a diagnosis helps or wastes money on testing and thyroid medication.

The finding adds pressure for science to settle this long-running controversy.

"We still don't have perfect answers," says Dr. Elizabeth Pearce, a well-known endocrinologist at Boston Medical Center, where a recent survey found widespread prenatal thyroid testing. But, "if it's my patient in my office, or it's me or my family member, I'm going to treat every time."

Obstetricians seem more wary.

"There are studies on both sides of the fence," says Dr. Dena Goffman of New York's Montefiore Medical Center, which tests only women at high risk. "If you don't know what to do with the results, you probably shouldn't order the test," she said.

The unassuming thyroid — a small bow tie-shaped gland nestled in the front of the neck — plays a big role in good health for everyone. It produces hormones that regulate metabolism and can affect almost every type of tissue in the body. About 20 million Americans are estimated to have a malfunctioning thyroid that, if serious enough, can contribute to heart disease, bone-thinning osteoporosis and infertility.

An overactive thyroid, called hyperthyroidism, speeds up bodily functions, causing such symptoms as weight loss, nervousness, anxiety and increased heart rate and vision problems.

Much more common is an underactive thyroid, called hypothyroidism. It slows body functions, causing such problems as fatigue, weight gain, depression, constipation and dry skin. It even can contribute to high cholesterol, according to the National Institutes of Health.