No link between maternal thyroid HT and children’s language, communication skills
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Children of mothers who received thyroid hormone therapy during pregnancy showed no difference in language and communication skill at age 8 years when compared with children of mothers who did not receive thyroid HT, according to findings published in JAMA Network Open.
“The treatment of maternal hypothyroidism during pregnancy could potentially reduce the incidence of language and communication delay in children up to 8 years after delivery,” Anna S. Frank, PhD, a postdoctoral research fellow at the University of Bergen, Norway, told Endocrine Today. “There is a need for a proper disease comparison group and an extension of the research to cover larger study populations, both nationally and internationally, to ensure that the conclusions are generalizable.”
Frank and colleagues analyzed data from 53,862 mother-child pairs using information from the Norwegian Patient Registry (mean age of mothers, 30 years; 26,145 girls; 27,717 boys) and 23,686 mother-child pairs participating in the population-based Norwegian Mother, Father and Child Cohort Study (MoBa), with data linked to the Norwegian Medical Birth Registry, the Norwegian Prescription Database and Norwegian Patient Registry (mean age of mothers, 31 years; 11,536 girls; 12,150 boys). Researchers stratified mother-child pairs into three groups: thyroid HT exposure during pregnancy (based on dispensed prescription records), unexposed to thyroid HT during pregnancy and mothers initiating thyroid HT after delivery. The researchers analyzed different outcome measures for the two study cohorts. For the Norwegian Patient Registry sample, outcome was defined by a diagnosis of language and speech impairment. For the MoBa sample, researchers followed children until age 8 years via parental self-completed questionnaires. Researchers used Cox proportional hazard models to estimate HRs for a language impairment diagnosis and used generalized linear models to estimate standardized mean score for parent-reported symptoms of language and communication deficits.
Within the Norwegian Patient Registry cohort, 1,204 pairs were exposed to thyroid HT (2.2%) and 1,376 mothers initiated thyroid HT after delivery (2.6%). Within the MoBa cohort, 532 pairs were exposed to thyroid HT (2.2%) and 594 mothers initiated thyroid HT after delivery (2.5%). During follow-up, the cumulative incidence of language and speech impairment diagnoses in children was 0.17% among children exposed to thyroid HT, 0.07% among children not exposed to thyroid HT and 0.13% among children of mother initiating thyroid HT after delivery.
The risk for a language and speech impairment diagnosis was numerically lower among children whose mothers received prenatal thyroid HT vs. children of unexposed women (adjusted HR = 0.75; 95% CI, 0.38-1.43) among children of mothers who initiated thyroid HT after delivery (adjusted HR = 0.63; 95% CI, 0.26-1.53), although numbers did not rise to statistical significance. Additionally, children of mothers who initiated thyroid HT after delivery received a diagnosis approximately 1 year earlier vs. children exposed to thyroid HT in utero and unexposed children (mean, 5.1 years vs. 6.4 years and 6.2 years, respectively).
“Compared with children of mothers who started thyroid hormone replacement therapy after delivery, children with prenatal thyroid hormone replacement therapy exposure seemed to have a reduced hazard (37% reduction) for language impairment; however, the 95% CI was wide and crossed the null,” the researchers wrote. “This hazard reduction was slightly greater in magnitude than the estimated 25% hazard reduction for thyroid hormone replacement therapy exposure vs. unexposed. This difference may be owing to the low number of diagnosis events in the group of mothers who started thyroid hormone replacement therapy after delivery. It is possible that mothers who initiated thyroid hormone replacement therapy after delivery might have developed postpartum hypothyroidism due to postpartum thyroiditis, although this possibility cannot be confirmed by the available data. Yet, if it holds true, it is likely that women who initiate thyroid hormone replacement therapy after delivery might have had thyroid antibodies already present during pregnancy.”
The researchers noted that the findings, while not reaching statistical significance, demonstrate that children of mothers who receive thyroid HT during pregnancy carry no increased risk for language impairments and support current recommendations that pregnant women with hypothyroidism should receive thyroid HT. – by Regina Schaffer
For more information:
Anna S. Frank, PhD, can be reached at the University of Oslo, Pharmacoepidemiology and Drug Safety Research Group, P.O Box 1068 Blindern, 0316 Oslo, Norway; email: asfrank88@gmail.com.
Disclosures: The authors report no relevant financial disclosures.
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