TUESDAY, June 22 (HealthDay News) -- Testing in the upper half
of what is currently considered a normal range for thyroid function
can nonetheless be problematic for pregnant women, who face an
increased risk for miscarriage as a result, new research
The study is the first to link what has previously been
considered normal thyroid function to miscarriage risk, according
to co-investigator Dr. Alex Stagnaro-Green, a senior associate dean
for education at the George Washington University School of
Medicine and Health Sciences in Washington, D.C.
The newly observed risk does not involve the presence of thyroid
peroxidase antibodies, something that prior research has linked to
a threat for miscarriage. An underactive thyroid has also been
associated with risk of miscarriage, the study authors noted in a
news release from the Endocrine Society.
"There has been an ongoing discussion as to whether or not the normal range for thyroid function tests is too broad," Stagnaro-Green said in the news release. "This study provides clear evidence that the normal range for thyroid function tests during pregnancy needs to be redefined."
The findings are scheduled for presentation Tuesday at the
Endocrine Society Annual Meeting and Expo in San Diego.
The researchers' concerns center on the use of the thyroid
stimulating hormone blood test. Since 2007, pregnant women reading
above the upper limit of 2.5 milli-international units per liter
(mIU/L) in the first trimester and 3 mIU/L in the second and third
trimesters have been deemed to have an "underactive thyroid," and
thus a higher risk for miscarriage.
However, the authors pointed out that many doctors do not
actually follow this guideline, instead relying on the non-pregnant
"normal range" marker of 4.5 or 5 mIU/L as an upper limit.
Stagnaro-Green and colleagues sought to get a handle on what
range is, in fact, safe for pregnant women, by tracking the
first-trimester thyroid tests and pregnancy outcomes of more than
4,100 women attending two community hospitals in Italy.
The team found that having a high-end normal-range thyroid
reading (above 2.5, but below 5) did not increase the risk for
having a pre-term delivery, however, miscarriage rates among women
with a high-normal range were "significantly higher" (about 6
percent versus 3.6 percent) than for women with the recommended
below-2.5 thyroid reading for pregnant women.
"This leads us to think that all pregnant women should be screened for thyroid function and any abnormalities treated," Stagnaro-Green concluded in the news release.
For more on thyroid disease in pregnancy, visit the
U.S. National Endocrine and Metabolic Diseases