Rates of pregnancy loss were substantially higher in women with first-trimester TSH levels of 2.5 to 5.0 mIU/L than in those with lower levels.
Consensus about what constitutes normal levels of thyroid-stimulating hormone (TSH) during pregnancy is shifting; moreover, the effects of subclinical hypothyroidism on maternal or neonatal health remain largely unknown. In a prospective study, researchers assessed pregnancy outcomes in women who were screened during the first trimester for TSH and thyroid-peroxidase antibody. All participants were negative for thyroid-peroxidase antibody; 3481 had TSH levels <2.5 mIU/L and 642 had TSH levels 2.5 to 5.0 mIU/L.
Women with TSH levels <2.5 mIU/L had lower rates of spontaneous pregnancy loss than did those with TSH levels 2.5 to 5.0 mIU/L (3.6% vs. 6.1%; P=0.006); rates of preterm delivery were similar between groups. In adjusted analysis, likel…