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Maternal TRAb levels predict neonatal hyperthyroidism
Serum thyroid-stimulating hormone receptor antibody, or TRAb, levels during the third trimester of pregnancy are a potential predictor for neonatal hyperthyroidism in children of women with Graves’ disease treated with radioiodine before conception, according to findings published in Thyroid.
“The serum TSH receptor antibody levels of Graves’ disease patients is known to increase after [radioiodine] therapy and then typically decrease to the pre‐[radioiodine] therapy level within a year, but in some patients, they can remain elevated for years,” Ai Yoshihara, MD, PhD, of Ito Hospital in Tokyo, and colleagues wrote. “Maternal TRAbs transferred to the fetus through the placenta may stimulate the fetal thyroid gland starting as early as 18 weeks of pregnancy.”
To determine an incidence rate of neonatal hyperthyroidism among women treated for Graves’ disease, Yoshihara and colleagues conducted a retrospective case review of 145 women with the condition who became pregnant within 2 years after receiving radioiodine therapy. All births occurred between April 2004 and Dec. 21, 2015. The researchers based the diagnosis of neonatal hyperthyroidism on TSH and free thyroxine levels in cord blood samples or blood samples taken within a week after birth.
A neonatal hyperthyroidism incidence rate of 5.5% was found for the entire cohort with higher rates observed with more recent radioiodine therapy. The rate was 8.8% for children born to mothers who had radioiodine therapy at 6 to 12 months before conception, 5.5% at 12 to 18 months and 3.6% at 18 to 24 months. Compared with women whose children did not have neonatal hyperthyroidism, those whose children had the condition had higher serum TRAb levels at the time of radioiodine therapy (40 IU/L vs. 9.7 IU/L; P = .0034) and during the first (40 IU/L vs. 6 IU/L; P < .0001) and third trimesters of pregnancy (22.4 IU/L vs. 2.4 IU/L; P < .0001).
The researchers noted a negative correlation between serum TRAb levels in the first trimester and the number of days between radioiodine therapy and conception (P = .0011). Additionally, TRAb levels in the third trimester were determined to be the lone risk factor for neonatal hyperthyroidism. Based on that information, the researchers determined that a serum TRAb level of 9.7 IU/L or more in the mother during the third trimester was a strong predictor of neonatal hyperthyroidism. Additional analysis determined that a level up to 28 IU/L in the first trimester was predictive of a third trimester level of less than 9.7 IU/L. – by Phil Neuffer
Disclosures: The authors report no relevant financial disclosures.
Editor’s note: This article was updated on Jan. 2, 2019, to clarify that the article is about the incidence of neonatal hyperthyroidism, not hypothyroidism. We regret the error.