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 (TPOAb) 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.