Hypothyroidism in Pregnant Woman May Raise Child's Risk of ADHD

By Linda Carroll

October 23, 2020

(Reuters Health) - Low levels of maternal thyroid hormone during the first three months of pregnancy may influence a fetus's brain development leaving the child at a greater risk of attention-deficit hyperactivity disorder (ADHD), a new study suggests.

In an analysis of data from more than 300,000 children born at Kaiser Permanente Southern California hospitals, researchers found that when pregnant women had low levels of thyroid hormone during the first trimester, there was a 28% increase in the risk of ADHD in their offspring, according to the results published in the American Journal of Perinatology.

"Thyroid health early in pregnancy is very important to neurological development in a woman's offspring," said the study's lead author, Morgan Peltier, an associate professor in the departments of clinical obstetrics, gynecology and reproductive medicine at NYU Langone's NYU Winthrop Hospital in New York City. "The effects might not be apparent at birth, but they can be lasting."

Peltier and his colleagues analyzed the electronic medical records from 571,674 births between January 1, 2000 and December 31, 2016 to Kaiser Permanente Southern California (KPSC) members in all KPSC hospitals.

The records included information on perinatal service (obstetrical conditions and procedures, fetal/neonatal outcomes), maternal and child inpatient/outpatient medical care, laboratory and pharmacy records, maternal sociodemographic and behavioral characteristics, the child's race/ethnicity, age, and gender. Parental demographic and maternal medical and obstetric health records were linked to the children's medical records using medical record numbers unique for each pregnancy.

The researchers excluded 130,556 births due to reasons including: multiple births, stillbirths, gestation shorter than 28 weeks, or longer than or equal to 43 weeks, the child leaving KPSC prior to age 3, autism diagnosis, and ADHD diagnosis prior to age 3 but not confirmed at later age.

That left 16,696 children diagnosed with ADHD and 312,461 without the disorder, all of whom were followed up to age 17.

Of the 329,157 pregnancies followed in the study, 9,675 (2.9%) had a diagnosis of hypothyroidism. Women who gave birth to children with ADHD were younger than those with non-ADHD children, tended to finish high school, but were more likely to make less than $30,000 per year.

When the researchers accounted for factors that might impact the risk of ADHD, they found that, overall, prenatal exposure to hypothyroidism was significantly associated with increased risk of ADHD and "the trend was largely confined to the first trimester," the authors note.

The findings suggest that children whose mothers were low in thyroid hormone during pregnancy "might benefit from enhanced screening for ADHD and other neurodevelopmental disorders," Peltier said. "A lot of growth factors that mediate brain development, including myelination and the creations of synapses, are regulated by thyroid hormone."

The new study takes on a "very controversial area," said Dr. Terry Davies, an expert on hypothyroidism in pregnancy, Baumritter professor of medicine at the Icahn School of Medicine at Mount Sinai in New York City, and past president of the American Thyroid Association.

"The literature has been quite confusing, but this is a very large study and so I think there is a potentially important message," Dr. Davies said. "This is another piece of information adding to the data on more severe thyroid failure causing neurodevelopmental problems."

"The risk found in this study is small but I think it suggests once again that the thyroid status of any woman who is planning to become pregnant or is pregnant is of great concern," Dr. Davies said. "The professional societies still do not recommend routine screening of women for their thyroid function, which I think is going against the evidence."

While women can be screened for hypothyroidism when they come in for their first prenatal visit, that may be too late, Dr. Davies said. "Women often don't appear until the 10th or 12th week of pregnancy, and that means the first trimester is gone," he added. "The major period of brain development has already passed. Neuronal cells are dependent on thyroid hormone for normal differentiation, processing and brain building. There's no doubt that the brain needs thyroid support, it's full of thyroid hormone receptors."

SOURCE: https://bit.ly/2Tk2mf7 American Journal of Perinatology, online October 21, 2020.