Maternal TSH and FT4 trajectories and preschoolers’ behaviors
Previous studies have reported that during pregnancy, maternal subclinical hypothyroidism (elevated TSH with normal FT4) as well as isolated hypothyroxinemia (decreased FT4 with normal TSH) are associated with adverse maternal and child outcomes, including preterm delivery and low birth weight.
However, most studies have not determined maternal thyroid hormone levels in different trimesters.
Researchers recruited pregnant women going for their first antenatal checkup at the Ma’anshan Maternal and Child Health Hospital in China from May 2013 to September 2014 and identified 1,860 mother-child pairs.
They determined maternal thyroid hormone levels from blood samples taken during the first, second, and third trimester: on average, gestational week 10, 25, and 34, respectively.
The researchers found that TSH levels increased somewhat from trimester 1 to trimester 2 and then decreased slightly in trimester 3. Most women (68%) had a low TSH trajectory, 28% had a moderate TSH trajectory, and 4% had a high TSH trajectory.
FT4 levels dropped sharply from trimester 1 to trimester 2 and then increased somewhat in trimester 3. About half of the women (52%) had a moderate FT4 trajectory, 33% had a low FT4 trajectory, and 15% had a high FT4 trajectory.
Most women (96.5%) had a low and stable TPOAb level, and the rest (3.5%) had high and decreasing TPOAb levels.
When the children in the study were 4 years old, their main caregiver (parent or grandparent) completed the 100-question Achenbach Child Behavior checklist to identify whether the child often, sometimes, or never displayed three internalizing problem behaviors (emotionally reactive, anxious/depressed, or withdrawn) and/or two externalizing problem behaviors (attention problems or aggressive behavior).
Study limitations, more research needed
It is not clear why the associations between maternal hormones and offspring behavior were only seen in boys. Perhaps male fetuses are more sensitive than female fetuses to changing maternal thyroid hormone levels in pregnancy, the researchers speculate.
They acknowledge that study limitations include there were few children with aggressive behavior, so the confidence interval for the association of the moderate TSH trajectory with aggressive behavior was very wide.
In addition, evaluation of children’s behavior by caregivers was subjective. Also, the researchers did not have information about iodine levels, and low iodine levels can impair child brain development.
And there may have been residual confounders that researchers did not account for, such as differences in family upbringing, parental marital status, and the mother’s exposure to endocrine disruptors.
Therefore, further research is needed.
The study was supported by grants from the National Natural Science Foundation of China, the University Synergy Innovation Program of Anhui Province, the Sci-Tech Basic Resources Research Program of China, the National Key Research and Development Program, the Chinese Academy of Medical Sciences, and the Research Fund of Anhui Institute of Translational Medicine. The researchers and Dr. Nguyen have reported no relevant financial relationships.
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