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Thyroid Biology and Disease

SAT-348 - Levothyroxine in Pregnant Women with Subclinical Hypothyroidism: Effects on Obstetric and Neonatal Outcomes: A Systematic Review and Meta-Analysis

Saturday, June 13, 2026
9:30 AM - 4:30 PM CT


Introduction: During pregnancy, increased metabolic demands place significant strain on thyroid function, as the maternal thyroid remains the primary source of thyroid hormones until approximately 16–20 weeks of gestation. Inadequate adaptation to this demand may result in subclinical hypothyroidism (SCH), characterized by elevated thyroid-stimulating hormone (TSH) levels with normal free thyroxine (fT4), affecting approximately 2–5% of pregnancies. Levothyroxine (LT4) is considered the standard treatment; however, its clinical benefits remain controversial due to inconsistent evidence and conflicting guideline recommendations.

Objective: To evaluate the effects of LT4 treatment in pregnant women with SCH on obstetric and neonatal outcomes.

Methods: A systematic review and meta-analysis were conducted following PRISMA 2020 guidelines using PubMed, Embase, and Cochrane Library. Comparative studies evaluating levothyroxine (LT4) versus placebo or no treatment in pregnant women with subclinical hypothyroidism were included. Effect sizes were calculated using odds ratios (OR) and mean differences (MD) with a random-effects model.

Results: Twenty-four studies involving 6,255 women were included in the meta-analysis. LT4 treatment demonstrated consistent neonatal benefits, including higher birth weight, lower rates of IUGR, reduced NICU admissions, and decreased pregnancy loss (RR = 0.56; 95% CI: 0.42–0.75). No significant overall reduction in preterm birth was observed, nor were there significant differences in miscarriage or gestational hypertension. Subgroup analyses suggested a trend toward reduced preterm birth among women with TSH levels >4.0 mIU/L (RR = 0.47), which was not observed in the 2.5–4.0 mIU/L group. Anti-TPO status also appeared to influence treatment response. LT4 use was associated with higher rates of gestational diabetes (OR ≈ 3.43), likely reflecting confounding by indication. Individual patient data analyses suggested that adverse pregnancy outcomes were more strongly associated with low fT4 levels than with isolated TSH elevation.

Conclusion: LT4 treatment in pregnant women with SCH is associated with consistent neonatal benefits, particularly regarding birth weight, IUGR, NICU admission, and pregnancy loss, but does not demonstrate a robust reduction in preterm birth. Its effectiveness appears to vary according to baseline TSH levels and anti-TPO status, supporting a more individualized therapeutic approach. Further well-designed randomized controlled trials are needed to clarify its clinical role and optimize treatment recommendations

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