Subclinical Hypothyroidism Increases Gestational Diabetes Risk

June 05, 2012

By Will Boggs MD

NEW YORK (Reuters Health) Jun 04 - Higher thyrotropin levels are associated with an increased risk of developing gestational diabetes, according to a report in the May 2012 Obstetrics & Gynecology.

"Although we found a relationship between subclinical hypothyroidism and gestational diabetes, we do not advocate routine prenatal thyroid screening in asymptomatic women or in those with gestational diabetes," Dr. Carmen M. Tudela from University of Texas Southwestern Medical Center, Dallas, Texas told Reuters Health by email. "In women with a history of subclinical hypothyroidism, we also do not recommend early gestational diabetes screening. Further studies related to subclinical thyroid disease in pregnancy must be performed before these recommendations should change."

Dr. Tudela and colleagues estimated the effects that subclinical thyroid dysfunction may have on the incidence of gestational diabetes in a 30-month study of 24,883 women who delivered a singleton fetus weighing more than 500 g.

Most women (95.5%) were euthyroid. Only 2.1% met criteria for subclinical hypothyroidism (thyrotropin level above 4.13 mU/L and normal serum free thyroxine, or T4, level. The remaining women (2.3%) met criteria for subclinical hyperthyroidism (subnormal thyrotropin levels with normal serum free T4 levels).

The rate of gestational diabetes was higher in women with subclinical hypothyroidism (6.3%) compared to euthyroid women (4.2%) and women with subclinical hyperthyroidism (2.2%).

After adjusting for other factors, the risk for gestational diabetes was significantly lower in women with subclinical hyperthyroidism, but the increased risk of gestational diabetes in women with subclinical hypothyroidism was no longer significant.

In a logistic regression model, however, thyrotropin was a significant predictor of gestational diabetes after adjusting for maternal factors of age, weight, race, and parity.

"At our institutions, we use the targeted screening for thyroid disease in women that is employed by most obstetricians in the United States and is currently recommended by the American College of Obstetricians and Gynecologists," Dr. Tudela said. "These guidelines include screening women with a history of thyroid disorders and those that are symptomatic."

"Most obstetricians are already testing all pregnant women for gestational diabetes," Dr. Tudela added, "but it is premature to recommend additional testing to diagnose subclinical hypothyroidism in women with gestational diabetes based on our study findings."


Obstet Gynecol 2012;119:983-988.


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