This article is more than 5 years old. Information may no longer be current.
Levothyroxine fails to increase IQ in offspring of women with subclinical thyroid disease
Cognitive outcomes in children through age 5 years born to women with subclinical hypothyroidism or hypothyroxinemia were not significantly improved with levothyroxine treatment compared with placebo, according to published findings.
“After more than a decade of study, including a comprehensive testing battery through 5 years of age, we can find no evidence that children of women with either subclinical hypothyroidism or isolated hypothyroxinemia during pregnancy benefit from thyroid hormone replacement,” Brian M. Casey, MD, director of the division of maternal-fetal medicine, chief of obstetrics at Parkland Hospital and professor, department of obstetrics and gynecology at University of Texas Southwestern, told Endocrine Today. “Nor did we find any impact of treatment on pregnancy and neonatal outcomes.”
Casey and colleagues evaluated data on women with subclinical hypothyroidism (n = 677) or hypothyroxinemia (n = 526) who underwent thyroid screening from October 2006 to October 2009 to determine the effect of screening and thyroxine replacement duration pregnancy on the IQ of children at age 5 years. Participants with subclinical hypothyroidism were randomly assigned to levothyroxine (n = 339) or placebo (n = 338), as were participants with hypothyroxinemia (levothyroxine, n = 265; placebo, n = 261).
Randomization occurred before 17 weeks’ gestation in the subclinical hypothyroidism group and before 18 weeks’ gestation in the hypothyroxinemia group.
There were no statistically significant differences in mean gestational age at delivery or in overall and serious adverse events between either group whether assigned to levothyroxine or placebo.
In the subclinical hypothyroidism group, median IQ score in the offspring was 97 among participants assigned levothyroxine and 94 in participants assigned placebo. In the hypothyroxinemia group, medial IQ score in the offspring was 94 in participants assigned levothyroxine and 91 in participants assigned placebo.
“Together with the results of a previous large study from the United Kingdom, it seems clear that screening during pregnancy for subclinical hypothyroidism and treatment does not result in improved pregnancy, neonatal or developmental outcomes,” Casey said. “New mothers-to-be should be very reassured. Based on our study findings, there is no reason for them to undergo another routine test during pregnancy to look for thyroid abnormalities or to worry that their baby will have neurodevelopmental delay if they have or had subclinical thyroid disease and weren’t treated with thyroid hormone replacement. In our study, both those women that were treated with thyroid hormone and those that weren’t had children with normal IQ scores at 5 years of age, and there was no difference in their scores according to treatment group.”
In an accompanying editorial, David S. Cooper, MD, of the division of endocrinology, diabetes and metabolism, Johns Hopkins University School of Medicine, and Elizabeth N. Pearce, MD, of the section of endocrinology, diabetes and nutrition, Boston University School of Medicine, wrote that “screening and treatment for subclinical hypothyroidism, if performed well into the second trimester of pregnancy, are unlikely to be beneficial.”
“However, because more than 75% of women in the United States have their first prenatal visit before 12 weeks of gestation, earlier treatment appears to be feasible,” they wrote. “We continue to endorse the recent guidelines of the American Thyroid Association, since the early initiation of low-dose levothyroxine therapy for subclinical hypothyroidism may be of benefit, is inexpensive, and is unlikely to be harmful.” – by Amber Cox
For more information:
Brian M. Casey, MD, can be reached at brian.casey@utsouthwestern.edu.
Disclosure: Casey and Cooper report no relevant financial disclosures. Pearce reports personal fees and non-financial support from Merck Serono and IBSA Institut Biochimique SA.