Maternal Early-Pregnancy Thyroid Function Is Associated With Subsequent Hypertensive Disorders of Pregnancy: The Generation R Study

Context: Hypertensive disorders during pregnancy are associated with a wide range of maternal and fetal complications, and only a few risk factors are known for the development of these disorders during pregnancy. Conflicting and limited data are available on the relationship between thyroid (dys) function and the risk of hypertensive disorders of pregnancy. Objective: The objective of the investigation was to study the associations between early-pregnancy thyroid dysfunction, thyroid function within the normal range, and the risk of hypertensive disorders. Design, Setting, and Participants: In early pregnancy, serum TSH, free T-4 (FT4), and thyroperoxidase antibody (TPOAb) levels were determined in 5153 pregnant women. No interventions were done. The associations of thyroid function with the risk of hypertensive disorders were studied. Main Outcome Measures: Mean blood pressures and hypertensive disorders, including pregnancy-induced hypertension (n = 209) and preeclampsia (n = 136), were measured. Results: Hyperthyroid mothers had a higher risk of hypertensive disorders [odds ratio (OR) 3.40 [95% confidence interval (CI) 1.46-7.91], P = .005], which was mainly due to an increased risk of pregnancy-induced hypertension [OR 4.18 (95% CI 1.57-11.1), P = .004]. Hypothyroidism and hypothyroxinemia were not associated with hypertensive disorders. Within the normal range, the high-normal FT4 levels were associated with an increased risk of hypertensive disorders [OR 1.62 (95% CI 1.06-2.47), P = .03], which was mainly due to an increased risk of preeclampsia [OR 2.06 (95% CI 1.04-4.08), P = .04]. The TPOAb status was not associated with hypertensive disorders. Conclusions: We show that biochemical hyperthyroidism and also high-normal FT4 levels during early pregnancy are associated with an increased risk of hypertensive disorders. These data demonstrate that these associations are even seen for a mild variation in thyroid function within the normal range.