Thyroid Dysfunction and Autoantibodies During Pregnancy as Predictive Factors of Pregnancy Complications and Maternal Morbidity in Later Life

Although it has been hypothesized that maternal thyroid dysfunction and/or positive thyroid antibodies during gestation are associated with certain pregnancy complications and an increased risk of later maternal cardiovascular diseases or diabetes, existing data is inconsistent. The aim of this population-based cohort study was to investigate the association between maternal thyroid dysfunction and/or antibodies detected during pregnancy and the occurrence of pregnancy complications or later maternal hypertension, diabetes, and thyroid disease over a 20-year follow-up period. The study population was comprised of mothers with singleton pregnancies who enrolled in the Northern Finland Birth Cohort 1986 and had sufficient early pregnancy serum samples in storage (n = 5805); these were tested for thyroid function and antibody analyses. Data from 3 registries were obtained to determine the health of these women in the 20 years since their index pregnancy; data included whether these women had diseases requiring medication, as well as hospital discharge diagnoses and causes of death. Women whose tested serum samples had results consistent with thyroid dysfunction (n = 786) were grouped into 5 categories (overt hypothyroidism, subclinical hypothyroidism, subclinical hyperthyroidism, overt hyperthyroidism, and hypothyroxinemia) and compared to women with normal thyroid function tests (n = 4719) who served as controls. The primary outcome measures were pre-eclampsia and gestational diabetes during the index pregnancy, later morbidity (maternal hypertension, diabetes, and thyroid disease), and total mortality. No association was found between thyroid dysfunction or thyroid antibodies and preeclampsia or gestational diabetes. The most important factor that predicted subsequent thyroid disease was overt hypothyroidism during pregnancy, with more than a 17-fold independent risk (hazard ratio [HR]: 17.7; 95% confidence interval [CI]: 7.8–40.6). Overt hypothyroidism during gestation was also associated with a 6-fold increased risk of diabetes (HR: 6.0; 95% CI: 2.2–16.4). Other predictive risk factors associated with later thyroid disease included subclinical hypothyroidism (HR: 3.3; 95% CI: 1.6–6.9), thyroid peroxidase antibody positivity (HR: 4.2; 95% CI: 2.3–7.4), and thyroglobulin antibody positivity (HR: 3.3; 95% CI: 1.9–6.0). There was no association between thyroid dysfunction or antibodies during pregnancy and later hypertension or overall mortality. The findings indicate that hypothyroidism and thyroid antibodies in early pregnancy are predictive risk factors for subsequent thyroid disease. Overt hypothyroidism during pregnancy seems to be a major risk factor for the development of diabetes.