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Certain thyroid hormone patterns in mothers were tied to behavioral development in young boys, a birth cohort study suggested.

Among nearly 2,000 mother-child pairs, boys born to mothers with high thyroid-stimulating hormone (TSH) levels during pregnancy had a two times higher chance of being withdrawn in preschool (OR 2.01, 95% CI 1.16-3.50), reported Kun Huang, PhD, of Anhui Medical University in China, and colleagues.

A high maternal TSH level during pregnancy was also significantly associated with externalizing problems in preschool-age boys (OR 2.69, 95% CI 1.22-5.92), the group wrote in the .

Even moderate TSH trajectories were linked to a higher risk of exhibiting aggressive behaviors among boys (OR 3.76, 95% CI 1.16-12.23).

TSH wasn't the only thyroid hormone tied to young boys' behavioral development, as moms who had high free thyroxine (FT4) trajectories were more likely to have boys who struggled with anxiety- and depression-related symptoms (OR 2.22, 95% CI 1.08-4.56). A high maternal FT4 trajectory was also linked with a greater number of total behavioral problems in preschool boys (OR 1.74, 95% CI 1.13-2.66).

On the other end of the spectrum, moms who had a low FT4 trajectory during pregnancy were over four times more likely to have boys who exhibited aggressive behaviors around preschool-age (OR 4.17, 95% CI 1.22-14.24).

Interestingly, none of these behavioral associations were seen in girls.

"Our findings highlight the significance of close monitoring and management of maternal thyroid function during pregnancy," Huang said in a statement. "This research presents a new perspective in early intervention of children's emotional and behavioral problems."

The researchers pointed out that many previous studies have connected the dots between maternal subclinical hypothyroidism -- an elevated TSH with normal FT4 -- as well as isolated hypothyroxinemia -- decreased FT4 with normal TSH -- during pregnancy with several adverse maternal and child outcomes, like and .

Prior data have also suggested a link between maternal hyperthyroidism or hypothyroidism with offspring's , leading to conditions such as ADHD and epilepsy.

While the exact biological mechanism underpinning these associations is "unclear," the researchers did suggest that elevated TSH concentrations during pregnancy may lead to thickening of the frontal and parietal cortex in children, thus impacting their behavioral development.

Huang's group collected data from the Ma'anshan Birth Cohort in China, which included pregnant women recruited from May 2013 to September 2014. Women with a personal or family history of thyroid disease were excluded.

Thyroid hormones were assessed via fasting venous blood during routine antenatal checkups during the first trimester (average 10 gestational weeks), second trimester (average 25 gestational weeks), and third trimester (average 34 gestational weeks) of pregnancy. The researchers noted that they used thyroid hormone trajectories, which considered repeated measures during the trimesters since hormones are "dynamic during pregnancy" and may be a "better predictor of children's behavioral problems than assessment of thyroid function during a single trimester."

Split into three categories, 4.4% of women had high TSH levels during pregnancy, 27.8% had moderate levels, and 67.8% had low levels. As for FT4, 14.6% had high levels, 52.4% had moderate levels, and 33% had low levels.

Children's behavioral development was measured with the Achenbach Child Behavior Checklist around the age of 4.

One limitation to the study was an inability to rule out environmental factors that may play a role in the behavioral development of children.

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