Maternal and fetal outcomes in pregnancies with abnormal trimester-specific thyroid-stimulating hormone levels receiving early levothyroxine therapy: a prospective cohort study

INTRODUCTION: The effect of maternal subclinical and overt hypothyroidism on pregnancy outcomes remains controversial. Prospectivedata on outcomes in women with trimester-specific thyroid-stimulating hormone (TSH) abnormality who received early empiric levothyroxine(LT4) therapy are limited. MATERIAL AND METHODS: In this prospective cohort study, 295 pregnant women whose TSH level at the first antenatal visit was outsidethe 2017 American Thyroid Association (ATA) trimester-specific reference ranges (cases) and 283 euthyroid pregnant women (controls)were enrolled at a tertiary internal medicine outpatient clinic. All cases received LT4 regardless of thyroid peroxidase (TPO) antibodystatus. Multivariable logistic regression adjusted for age, body mass index (BMI), gravidity, and anti-TPO positivity was performed. RESULTS: Groups were comparable for age, BMI, gravidity, and parity (all p > 0.05). Overall composite complication rates were similar (49.8% vs. 45.6%, p = 0.348). However, oligohydramnios (7.1% vs. 2.8%, p = 0.030) and miscarriage (2.4% vs. 0.0%, p = 0.015) were significantlymore frequent in cases, with no miscarriage events occurring in the euthyroid control group. In adjusted analysis, case-group membershipwas an independent risk factor for oligohydramnios (aOR = 3.41; 95% CI: 1.42-8.19; p = 0.006). Within the case group, anti-TPOpositivity was an independent predictor of polyhydramnios (aOR = 3.93; 95% CI: 1.03-15.01; p = 0.046), and anti-TPO-positive womenrequired higher LT4 doses and delivered earlier (both p ≤ 0.001). CONCLUSIONS: Early LT4 therapy in trimester-specific TSH abnormality preserves overall pregnancy outcomes; however, residual risks of oligohydramnios and miscarriage warrant close monitoring. Anti-TPO positivity identifies a distinct phenotype with a higher treatmentrequirement and a propensity for polyhydramnios.