Comparison of fetal thyroid measurements between treated subclinical hypothyroidism and euthyroid pregnancies: A prospective observational study

Aim. To investigate the impact of maternal subclinical hypothyroidism (SCH) treated with levothyroxine on fetal thyroid dimensions during pregnancy. Materials and Methods. In this prospective observational study, 50 pregnant women with treated SCH and 52 euthyroid controls underwent ultrasonographic evaluation between 20 and 39 gestational weeks. Fetal thyroid circumference (FTC) and fetal thyroid area (FTA) were measured, and correlations with maternal TSH levels and levothyroxine dosage were analyzed. Results. No significant differences were found in fetal thyroid measurements between the SCH and control groups, both before and after adjustment for gestational age. Correlation analyses revealed negligible associations between maternal thyroid function parameters and fetal thyroid size. While levothyroxine dose showed a weak negative trend with fetal thyroid measurements, this was not statistically significant. The amniotic fluid index (AFI) was significantly higher in the SCH group despite treatment. Conclusion. Adequately treated maternal SCH does not appear to affect fetal thyroid development. These findings support the importance of early diagnosis and levothyroxine therapy to normalize maternal thyroid function and potentially protect fetal outcomes.