The relation between gestational thyroid parameters and depression: A reflection of the downregulation of the immune system during pregnancy?

Objective: To assess the relation between thyroid parameters and an episode of major depression at different trimesters during pregnancy, taking into account possible confounders. Design: Prospective follow-up of 1017 pregnant women from the general population with assessment of thyroid parameters and depression using syndromal diagnosis interviews at 12, 24, and 36 weeks' gestation. Main outcome: The prevalence of major depression decreased from 5.3% to 2.9%, and that of elevated concentrations of thyroid peroxidase antibody (TPO-Ab) titers from 8.4% to 6.5% toward the end of term. Subclinical hyperthyroidism not related to TPO-Ab (odds ration [OR] 3.6; 95% confidence interval [CI]: 1.2-0.2) and TPO-Ab (OR 2.1; 95% CI: 1.1-5.8) at 12 weeks' gestation, and TPO-Ab (OR 2.8; 95% CI 1.9-7.1) at 24 weeks' gestation were independently related to major depression. Anxiety and the occurrence of stressful life events were related to depression at all trimesters. Conclusions: The occurrence of major depression and high titers of TPO-Ab show a similar pattern of decline throughout pregnancy. During early gestation, thyroid autoimmunity seems to be related to depression while at the end of term-when there is maximal downregulation of the immune system-autoimmunity does not seem to play an important role with regard to the occurrence of depression.