WASHINGTON - Pressure is increasing for science to settle a long-running controversy about mild thyroid problems and pregnancy.

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.

The problem is that while serious cases are treated with a hormone pill, so far there's little evidence that treating the milder cases makes a difference.

Researchers at Quest Diagnostics recently examined records for half a million pregnant women. Of those who got tested, a higher-than-expected number - 15 percent - had an underactive thyroid, mostly mild cases. But that's five-fold higher than some previous estimates. The study is in the Journal of Clinical Endocrinology & Metabolism.

A well-known endocrinologist at Boston Medical Center says she would treat an underactive thyroid "every time."

But obstetricians seem more wary, noting there are conflicting studies about mild problems.