TPO and hypothyroidism: Sensitivity and stratification analyses indicated that thyroperoxidase antibody (TPOAb) positivity in the first trimester (odds ratio [OR], 1.49; 95% confidence interval [CI], 1.17–1.90) and overt hypothyroidism restricted to women negative for TPOAb (OR, 4.94; 95%CI: 1.64–14.84) was associated with an increased risk of preterm birth.