Subclinical hypothyroidism in early pregnancy linked to higher risk of overt hypothyroidism

A new study has shown that subclinical hypothyroidism diagnosed before 21 weeks of gestation is associated with pregnancy rates more than four times higher than overt hypothyroidism or thyroid replacement therapy within 5 years of delivery. The study is published in the peer-reviewed journal Thyroid, the official journal of the American Thyroid Association.

Subclinical hypothyroidism , or a change in thyroid-stimulating hormone (TSH) levels that is not severe enough to cause symptoms, is particularly common during pregnancy, affecting up to 1 in 4 pregnant women. Although subclinical hypothyroidism is not dangerous in itself, overt hypothyroidism is accompanied by serious symptoms, including fatigue, depression and of heart problems.

Michael Varner, MD, professor of obstetrics and gynecology at the University of Utah Health Spencer Fox Eccles School of Medicine, and co-authors reported that progression to overt hypothyroidism was more common in individuals with thyroid-stimulating hormone levels that were more than twice the normal range.

People with higher levels of antibodies to a thyroid enzyme, which may indicate that the body is developing an autoimmune response against the thyroid, also had a higher risk of hypothyroidism within 5 years of giving birth, compared with those with lower antibody levels.

Investigators found that diagnosis of hypothyroxinemia, a deficiency of the thyroid hormone thyroxine, before 21 weeks of gestation was not associated with the development of overt hypothyroidism after delivery.

“Studying the long-term associations of test results, as well as the impacts of our interventions, during pregnancy on the health and well-being of mothers and children is a particularly important aspect of clinical research in perinatal medicine,” Varner said. “While the NICHD Maternal-Fetal Medicine Unit Network parent trials from which our data were derived showed no differences in neurodevelopmental outcomes at 5 years of age in children following prenatal treatment of subclinical hypothyroidism or hypothyroxinemia, our data provide further evidence for the postpartum period as a time when autoimmune diseasesin this case hypothyroidism, are more likely to be present."

More information : Michael W. Varner et al, Progression of gestational subclinical hypothyroidism and hypothyroxinemia to overt hypothyroidism after pregnancy: pooled analysis of data from two randomized controlled trials, Thyroid (2024). DOI: 10.1089/thy.2023.0616