Abstract: Objective: To evaluate whether levothyroxine treatment improves maternal and neonatal outcomes in pregnant women with subclinical hypothyroidism and assess the need for universal screening in asymptomatic pregnant women.
Design: Prospective, randomized, double-blind, placebo-controlled clinical trial.
Setting: Tertiary care hospital in western Maharashtra, India, from September 2020 to March 2022.
Participants: 440 asymptomatic pregnant women (18-42 years) with singleton pregnancies and subclinical hypothyroidism (TSH ?4.0 mIU/L with normal free T4) diagnosed between 8-20 weeks of gestation.
Interventions: Participants were randomized 1:1 to receive either levothyroxine therapy (n=220) starting at 1.6 ?g/kg/day with dose adjustments to achieve target TSH levels, or matching placebo (n=220). Monthly thyroid function monitoring was performed with blinded dose adjustments.
Main Outcome Measures: Primary maternal outcomes included pregnancy loss, gestational diabetes mellitus, hypertensive disorders, and mode of delivery. Primary neonatal outcomes included low birth weight, preterm delivery, low APGAR scores, and neonatal intensive care unit admission.
Results: Of 4,738 deliveries during the study period, 440 women (9.28%) had subclinical hypothyroidism. Baseline characteristics were well-matched between groups (mean age 27.6±4.1 years, mean TSH 4.04±0.70 mIU/L). No statistically significant differences were observed in any maternal or neonatal outcomes between treatment and placebo groups. Pregnancy loss occurred in 12.3% vs 12.7% (p=0.887), gestational diabetes in 25.9% vs 25.0% (p=0.780), hypertensive disorders in 21.4% vs 24.5% (p=0.456), and cesarean delivery in 25.9% vs 30.0% (p=0.368) in levothyroxine vs placebo groups, respectively. Low birth weight (15.5% vs 10.9%, p=0.189) and preterm delivery (10.0% vs 11.8%, p=0.582) rates were similar between groups.
Conclusions: Levothyroxine treatment for subclinical hypothyroidism during pregnancy did not improve maternal or neonatal outcomes. Universal screening for asymptomatic subclinical hypothyroidism in pregnancy cannot be recommended based on these findings.
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