Subclinical Hypothyroidism in Pregnancy and Adverse Maternal-Fetal Outcomes — A Prospective Observational Study

Abstract

Background: Subclinical hypothyroidism in pregnancy is defined as elevated TSH with normal free T4 and affects 2 to 5% of pregnancies. Its association with adverse maternalfetal outcomes is increasingly recognised but remains debated. Methods: A prospective cohort study enrolled 200 pregnant women screened for thyroid function in the first trimester at a tertiary obstetric centre in India during 2023. Outcomes were compared between 52 women with SCH (TSH above 4.0 mIU/L with normal fT4) and 148 euthyroid controls. Results: SCH prevalence was 26.0%. SCH women had higher rates of preeclampsia (17.3% vs 6.8%, p equals 0.028), gestational diabetes (19.2% vs 8.8%, p equals 0.044), preterm birth (21.2% vs 8.1%, p equals 0.012), low birth weight (23.1% vs 10.1%, p equals 0.018), and NICU admission (19.2% vs 7.4%, p equals 0.022). TSH above 10 mIU/L was associated with significantly worse outcomes than TSH 4 to 10 (p equals 0.008). Levothyroxine-treated SCH patients (73.1%) had fewer complications than untreated patients. Conclusion: SCH is prevalent in 26% of pregnancies and significantly increases adverse outcomes. Universal first-trimester thyroid screening and early levothyroxine treatment are recommended.