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Risk for maternal hyperthyroidism increases during early pregnancy, postpartum period
There is a greater risk for onset of hyperthyroidism among women during the early pregnancy period and the postpartum period, according to recent findings.
In the population-based cohort study, researchers utilized linked data from the Danish Civil Registration System and the Medical Birth Registry to evaluate 403,958 women in Denmark with a singleton birth and no multiple births between 1999 and 2008. The researchers evaluated incident cases of hyperthyroidism from age 15 to 45 years. They defined incident hyperthyroidism as cases in which women filled a minimum of two prescriptions for antithyroid drugs between 1997 and 2010.
The researchers found that hyperthyroidism was diagnosed in 3,673 participants from 1997 to 2010, with an overall maternal incidence rate of 65 per 100,000 women per year.
Analysis of hyperthyroidism incidence rates in and around pregnancy revealed significant variation. It was high in the first trimester of pregnancy (incidence rate ratio [IRR] vs. remaining study period=1.5; 95% CI, 1.09-2.06), very low in the last 3 months of pregnancy (IRR vs. remaining study period=0.26; 95% CI, 0.15-0.44) and peaked between 7 and 9 months postpartum (IRR vs. remaining study period=3.8; 95% CI, 2.88-5.02).
In a separate analysis, the researchers studies whether these variations in and around pregnancy applied in a general sense to autoimmune diseases. They found that the incidence patterns for rheumatoid arthritis and inflammatory bowel disease around pregnancy were not similar.
“The incidence of maternal hyperthyroidism varied widely in and around pregnancy and both early pregnancy and the postpartum period were associated with an increased risk of onset of hyperthyroidism,” the researchers wrote. “More studies are needed to corroborate an early pregnancy incidence peak of Graves’ hyperthyroidism. Notably, the incidence pattern appeared specific for hyperthyroidism when compared to [rheumatoid arthritis] and [inflammatory bowel disease], but further studies of autoimmune thyroid disease and other autoimmune disorders are needed to clarify the interaction between pregnancy and onset of disease and the possible differential mechanisms involved.”
Disclosure: The researchers report no relevant financial disclosures.