Risk for attention-deficit hyperactivity disorder (ADHD) was increased among children who were exposed to maternal hypothyroidism during the periconceptual period. These findings, from a retrospective review of medical records, was published in the American Journal of Perinatology.

Medical records of 329,157 births between 2000 and 2016 in the Kaiser Permanente Southern California database were analyzed. All diagnoses were made using the International Classification of Diseases.

A total of 16,696 children were diagnosed with ADHD and 312,461 were not. Women who gave birth to a child with ADHD tended to be younger (P <.001), finished high school (P <.001), made <$30,000 annually (P <.001), to be nulliparous (P <.001), deliver preterm (P <.001), and to smoke tobacco during pregnancy (P <.001).


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Among all pregnancies, 2.9% had a hypothyroidism diagnosis within 120 days before or during their pregnancy. Risk for ADHD diagnoses among children born to women with a hypothyroidism diagnosis was increased (adjusted hazard ratio [aHR], 1.24; 95% CI, 1.14-1.35). However, the increased risk was not observed among women who did not treat their hypothyroidism or who were on a low dose (<50 ug/d) thyroid supplementation regimen (aHR, 1.08; 95% CI, 0.75-1.57).

Higher doses of maternal thyroid supplementation significantly increased risk for ADHD (aHR, 1.26; 95% CI, 1.14-1.39).

Risk for an ADHD diagnosis was elevated among children of women who were diagnosed with hypothyroidism at 61-120 days pre-pregnancy and delivered their baby preterm (aHR, 1.42; 95% CI, 1.01-1.99), women who were diagnosed prior to pregnancy and delivered a baby boy (aHR, 1.30; 95% CI, 1.15-1.46), women who were diagnosed 1-60 days pre-pregnancy and were non-Hispanic white (aHR, 1.57; 95% CI, 1.24-2.00), or women who were diagnosed during the first trimester and were Hispanic (aHR, 1.71; 95% CI, 1.25-2.33).

This study was potentially limited by underlying biases of diagnosing ADHD among minority children. These data indicated that non-Hispanic white children were at increased risk for ADHD, although the lower rate of diagnoses among non-white children may have led to an underestimated risk.

The study authors concluded that children born to women who were diagnosed with hypothyroidism within a few months of or during early pregnancy and sought treatment for their symptoms, had an increased risk for delivering a baby who would eventually be diagnosed with ADHD.

Future studies which stratify women by their hypothyroidism type are needed to better understand the possible molecular mechanisms causing the association between hypothyroidism and ADHD.

Reference

Peltier M R, Fassett M J, Chiu V, et al. Maternal hypothyroidism increases the risk of attention-deficit hyperactivity disorder in the offspring [published online October 21, 2020]. Am J Perinatol. doi:10.1055/s-0040-1717073