Assessment of the effect of Levothyroxine on pregnancy outcome in pregnant women with subclinical hypothyroidism and negative thyroid peroxidase antibody

Context Currently, there is no consensus on universal thyroid screening and levothyroxine (LT4) treatment of pregnant women with subclinical hypothyroidism (SCH) who are negative for thyroid peroxidase antibody (TPOAb-). Objective We aimed to evaluate the benefits of LT4 treatment on pregnancy outcomes in SCH-TPOAb- women. Design This study was conducted within the framework of the Tehran Thyroid and Pregnancy Study. A single-blind randomized clinical trial was undertaken in pregnant women who were SCH-TPOAb-. Setting Prenatal care centers of the Shahid Beheshti University of Medical Sciences. Patients Using the thyrotropin (TSH) cut point of 2.5 mIU/L, 366 SCH-TPOAb- and 1092 euthyroid TPOAb- women were recruited. Intervention SCH-TPOAb- women were randomly assigned to two groups: group A (n = 183) who were treated with LT4 and group B (n = 183) who received no treatment. A total of 1,028 euthyroid TPOAb- women served as the control group (group C). Main Outcome Measure The primary outcome was the rate of preterm delivery. Results Using the TSH cutoff of 2.5 mIU/L, no significant difference in preterm delivery was observed between groups A and B [relative risk (RR): 0.86; 95% confidence interval (CI): 0.47 to 1.55; P = 0.61]. However, log-binomial model analysis based on a cut point of 4.0 mIU/L demonstrated a significantly lower rate of preterm delivery in LT4-treated women compared with those who received no treatment (RR: 0.38; 95% CI: 0.15 to 0.98; P = 0.04). Conclusions Despite no beneficial effect of LT4 therapy in reducing preterm delivery in SCH-TPOAb- women with a TSH cut point of 2.5 to 4 mIU/L, LT4 could precisely decrease this complication using the newly recommended cutoff =4.0 mIU/L.