Subclinical hypothyroidism during pregnancy, an asymptomatic condition marked by an imbalance in thyroid hormones, may be linked to an increased risk of developing hypothyroidism within five years after childbirth, according to a new analysis funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).
The study, conducted by Dr. Michael Varner and colleagues from the University of Utah Health Sciences Center, also found that pregnant individuals with elevated levels of antibodies against a thyroid enzyme, indicating an autoimmune attack on the thyroid, faced a higher risk of hypothyroidism in the years following delivery.
Hypothyroidism occurs when the thyroid gland fails to produce sufficient hormones, leading to symptoms such as fatigue, weight gain, cold intolerance, and depression. Effective management typically involves hormone replacement therapy with thyroxine. Untreated hypothyroidism during pregnancy is known to increase the risk of complications such as low birthweight and impaired neurocognitive development in newborns.
Subclinical hypothyroidism is characterized by elevated levels of thyroid-stimulating hormone (TSH) while thyroid hormone levels remain normal. Although it often does not present symptoms and may not necessitate treatment, it has the potential to progress to overt hypothyroidism. In the United States, subclinical hypothyroidism affects approximately 2 to 2.5 percent of pregnancies.
The NICHD Maternal-Fetal Medicine Units Network previously investigated the effects of treating subclinical hypothyroidism and hypothyroxinemia (low levels of thyroid hormone despite normal TSH) during pregnancy. These studies found no significant differences in pregnancy outcomes or infant neurocognitive development between treated and untreated groups.
For the current study, researchers analyzed data from participants who were not treated for these conditions during pregnancy. They assessed thyroid function at one year and five years postpartum.
Results indicated that 13.4 percent of participants with subclinical hypothyroidism developed hypothyroidism within one year of delivery, with the rate rising to 15.6 percent by five years. For those with hypothyroxinemia, 3.1 percent developed hypothyroidism within a year, increasing to 7.5 percent after five years. Most participants with newly diagnosed hypothyroidism were identified through the study’s laboratory tests, having not been previously diagnosed.
Furthermore, participants with subclinical hypothyroidism and high levels of thyroid peroxidase antibodies—indicating an autoimmune response against the thyroid—showed significantly higher rates of hypothyroidism both one year (26.7 percent) and five years (30.5 percent) after delivery compared to those with lower antibody levels (6.5 percent and 7.5 percent, respectively).
While the original study did not show differences in long-term neurodevelopmental outcomes in children from treated versus untreated pregnancies, the current findings underscore the importance of monitoring thyroid health postpartum. The researchers suggest that due to the potential for autoimmune thyroid disease development in the years following pregnancy, healthcare providers and individuals should consider testing for thyroid dysfunction if symptoms of low thyroid function arise.
“Given the increased risk of developing hypothyroidism after pregnancy, especially for those with elevated thyroid peroxidase antibodies, it is important for providers to remain vigilant and consider testing for thyroid disease in individuals experiencing symptoms,” Dr. Varner noted.
This research highlights the need for continued attention to thyroid health during the postpartum period, offering valuable insights for future clinical practices and patient management.
