Is hypothyroidism in pregnant women linked to ADHD in children? Study says it increases risk by 24%
Low levels of critical, body-regulating hormones in mothers during the first three months of pregnancy may interfere with the baby’s brain development, suggest researchers. These hormones are produced in the thyroid gland in the neck. Investigators have suspected that disruptions in their production, or hypothyroidism, may contribute to attention-deficit/hyperactivity disorder (ADHD), which is the most common neurodevelopmental disorder of children in the US. Now a research team has found that children whose mothers were diagnosed with hypothyroidism shortly before or during the early stages of pregnancy were 24% more likely to have ADHD than children whose mothers did not have the diagnosis.
The investigators believe that the results are strong enough to warrant careful monitoring of pregnant women with low thyroid hormone levels. “Children born to women that had hypothyroidism just prior to or in their first trimester of pregnancy could benefit from enhanced screening for ADHD as it may lead to earlier diagnosis, treatment and improved outcomes for the condition,” study lead author Dr Morgan Peltier told MEA WorldWide (MEAWW).
The authors also found that boys born to hypothyroid women were four times more vulnerable to ADHD than girls whose mothers had hypothyroidism. Hispanic children born to hypothyroid mothers had the highest risk of any ethnic group studied. “Our findings make clear that thyroid health likely has a much larger role in fetal brain development and behavioral disorders like ADHD than we previously understood,” emphasizes Peltier, who is an associate professor in the departments of clinical obstetrics, gynecology, and reproductive medicine at NYU Winthrop Hospital, part of NYU Langone Health.
Hypothyroidism, also called underactive thyroid, refers to a condition when the thyroid gland does not make enough thyroid hormones to meet the body’s needs. “About 4.6% of the US population, ages 12 and older, has hypothyroidism, although most cases are mild. That’s almost 5 people out of 100,” says the National Institute of Diabetes and Digestive and Kidney Diseases, which is part of the National Institutes of Health (NIH).
ADHD, a neurodevelopmental disability affecting 9.4% of children 2 to 17 years of age, is characterized by difficulties in executive function, inattention, hyperactivity, and impulsivity. According to experts. it is the most widespread behavior disorder of children and it increases the risk of other life-long problems such as substance abuse, relationship problems, poorer job and academic performance, riskier driving, criminality, and suicide rates.
To determine if hypothyroidism before, or during, pregnancy increases the risk of ADHD in the child and how the association may be modified by preterm birth, sex of the child, and race-ethnicity, the team followed 329,157 children from birth until age 17. They were all born in Kaiser Permanente Southern California hospitals. The report included people of diverse ethnic backgrounds. The long study period of nearly two decades allowed the researchers to better capture cases of ADHD in the children as they aged and progressed through school, according to Peltier. “It is the first, to our knowledge of such as study in the US where there are large ethnic differences, and to look at how the timing of diagnosis, preterm birth, child sex, and race-ethnicity can contribute to the association,” he adds.
The investigators analyzed children’s medical records and collected key information about their mothers, including age during pregnancy, race, and household income. All children were evaluated for ADHD using the same criteria, which the authors say helped to prevent inconsistencies in how cases of the disorder were identified.
According to the findings, overall 16,696 children were diagnosed with ADHD. Hispanic children, whose mothers had low thyroid hormone levels during pregnancy, had a 45% increased risk for the neurodevelopmental disorder compared with a 22% increased risk in White children whose mothers had the same condition. Once a pregnancy had reached the second trimester, a woman’s hypothyroidism had little effect on her children. Peltier suggests that a possible explanation is that by this point, the fetus has begun to produce its own thyroid hormones and so is less vulnerable to its mother's deficiencies.
“Hypothyroidism diagnosed prior to or during pregnancy increases the risk of ADHD in the children. The association was strongest when diagnosed during the first trimester. For children born preterm, there was a significantly increased risk of ADHD if their mothers were diagnosed before but not during pregnancy,” says the study published in the American Journal of Perinatology.
The researchers next plan to investigate whether hypothyroidism during pregnancy can raise the risk of other neurodevelopmental disorders, such as epilepsy, cerebral palsy, and difficulties with speech. They also intend to explore other factors that may increase the risk of ADHD in children, such as exposure during pregnancy to environmental toxins like flame retardants found in upholstered furniture, electronic devices, and other household appliances.