Public Release: 

Does treatment of subclinical hypothyroidism in pregnant women impact IQ in offspring?

Society for Maternal-Fetal Medicine

ATLANTA (Feb. 1, 2016)--On Feb. 4 at 8 a.m. EST, in the oral plenary session at the Society for Maternal-Fetal Medicine's annual meeting, The Pregnancy Meeting, in Atlanta, Brian Casey, M.D. with the Eunice Kennedy Shriver National Institute of Child Health and Human Development and Maternal-Fetal Medicine Unit will present findings from a 5-year follow-up study that looked at the treatment of pregnant women with subclinical thyroid dysfunction and whether, or not, that impacted the IQ of their children. The abstract received the Norman Grant award.

Subclinical thyroid dysfunction includes either an isolated elevation in thyroid stimulating hormone (subclinical hypothyroidism) or an isolated decrease in circulating free thyroid hormone (hypothyroxinemia). Pregnant women identified with either condition are believed to be at risk for several adverse outcomes in the mother and fetus like gestational diabetes, preterm birth, placental abruption, and stillbirth. Prior studies have also pointed to the role of thyroid hormone in normal development of the fetal brain and suggested an increased risk of lower scores on developmental testing or IQ tests in children of women who went untreated.

The study, titled Effect of Treatment of Maternal Subclinical Hypothyroidism or Hypothyroxinemia on IQ in Offspring set out to determine whether or not subclinical thyroid dysfunction plays a role in diminished IQ in children of mothers identified with either condition during pregnancy. The study consisted of a multicenter study including two randomized, double-masked, placebo-controlled treatment trials run in parallel. Women with a singleton pregnancy presenting for prenatal care before 20 weeks' gestation underwent thyroid screening. Eligible and consenting women with either subclinical hypothyroidism or hypothyroxinemia were randomized to thyroid hormone replacement or an identical placebo. Maternal thyroid function was assessed monthly and study drug was adjusted to achieve a prespecified treatment goal. Developmental testing of offspring was performed annually including IQ score at age five.

Between October 2006 and October 2009, 97,226 pregnant women underwent thyroid screening. There were 3,058 women (3.1%) identified with subclinical hypothyroidism, of which 677 were eligible and randomized. There were also 2,508 (2.9%) women identified with hypothyroxinemia and 526 were randomized. Together, a total of 1203 women were enrolled in both treatment trials. Remarkably, 5-year Wechsler Preschool and Primary Scale of Intelligence IQ scores were obtained in 1,110 (92.3%) of the 1203 offspring. The result was that treatment of women identified with either subclinical hypothyroidism or hypothyroxinemia during the first half of pregnancy did not improve cognitive outcome in offspring through five years of age.

"We now know that children of mothers identified with either subclinical hypothyroidism or hypothyroxinemia during pregnancy do not benefit from maternal thyroid hormone replacement," Casey explained. "These results confirm that routine thyroid screening during pregnancy is not warranted."

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A copy of the abstract is available at http://www.smfmnewsroom.org and below. For interviews please contact Vicki Bendure at Vicki@bendurepr.com 202-374-9259 (cell).

The Society for Maternal-Fetal Medicine (est. 1977) is the premiere membership organization for obstetricians/gynecologists who have additional formal education and training in maternal-fetal medicine. The society is devoted to reducing high-risk pregnancy complications by sharing expertise through continuing education to its 2,000 members on the latest pregnancy assessment and treatment methods. It also serves as an advocate for improving public policy, and expanding research funding and opportunities for maternal-fetal medicine. The group hosts an annual meeting in which groundbreaking new ideas and research in the area of maternal-fetal medicine are shared and discussed. For more information visit http://www.smfm.org.

Abstract 2: Effect of Treatment of Maternal Subclinical Hypothyroidism or Hypothyroxinemia on IQ in Offspring

Author: Brian Casey1
1for the Eunice Kennedy Shriver NICHD MFMU Network, Bethesda, MD

Objective: To determine whether treatment of pregnant women identified with either subclinical hypothyroidism or hypothyroxinemia in the first half of pregnancy improves cognitive function in offspring at five years of age.

Study Design: This multicenter study consists of two randomized, double-masked, placebo-controlled trials run in parallel. Women with a singleton gestation presenting for care before 20 weeks' gestation underwent thyroid screening using serum TSH and free T4. Women with a TSH ? 4.0 mU/L and a free T4 in the normal range (0.86-1.9 ng/dL) were considered to have subclinical hypothyroidism. Those with a normal TSH (0.08 - 3.99 mU/L) but a free T4 < 0.86 ng/dL were considered to have hypothyroxinemia. Eligible and consenting women were randomized to either levothyroxine replacement or an identical placebo. Maternal thyroid function was assessed monthly and study drug adjusted to attain TSH or free T4 goals. Sham adjustments in placebo were used to maintain blinding. Developmental testing of offspring was performed annually including DAS II at age 3-years and IQ score using WPPSI-III at 5 years of age. If an infant was lost to follow-up after 3 years of age, the DAS II was substituted for the primary outcome. If an infant died prior to 3-year testing they were assigned a score of zero. Sample size estimates for each strata were based on 80% power to detect a 5-point IQ difference between treatment groups.

Results: Between October 2006 and October 2009, 97,226 pregnant women underwent thyroid screening. There were 3,058 women (3.1%) identified with subclinical hypothyroidism, of which 677 (22.1%) were eligible and randomized. There were 2,805 women (2.9%) identified with hypothyroxinemia and 526 (18.8%) were eligible and randomized. The mean gestational age at randomization was 17 weeks. WPPSI-III scores at 5 years of age were obtained in 1,110 (92.3%) of the 1203 offspring, 23 children were lost to follow-up after DAS II testing, and 22 infants died prior to 3-year testing.

Conclusion: Treatment of women identified with either subclinical hypothyroidism or hypothyroxinemia during the first half of pregnancy did not result in improved cognitive outcome in offspring at 5 years of age.

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