Morphometric Analysis of the Human Fetal Thyroid Gland Across Gestation: A Cross-Sectional Study

Background: The thyroid gland is the first endocrine gland to develop during embryogenesis and plays an essential role in fetal growth, metabolism, and neurodevelopment. Morphometric evaluation of the fetal thyroid provides important baseline data for understanding normal development and identifying congenital abnormalities. Material and Methods: This observational cross-sectional study was conducted on 40 human fetuses aged 13–38 weeks gestation. Fetuses with gross malformations or congenital thyroid anomalies were excluded. General fetal morphometric parameters, including fetal weight, crown-rump length (CRL), abdominal circumference, and head circumference, were recorded. Thyroid morphometry included thyroid weight, bilateral lobe length, width, thickness, and isthmus dimensions. Fetuses were categorized into 13–21 weeks (n=17), 22–30 weeks (n=15), and 31–38 weeks (n=8) gestational groups. Data were analyzed using ANOVA and Pearson’s correlation coefficient. Results: All fetal and thyroid morphometric parameters increased significantly with advancing gestational age (p<0.0001). Mean thyroid weight increased from 0.202±0.072 g in the 13–21 weeks group to 0.869±0.107 g in the 31–38 weeks group. Mean right lobe length increased from 7.788±1.076 mm to 14.165±0.571 mm, while left lobe length increased from 7.636±1.061 mm to 14.047±0.759 mm. Strong positive correlations were observed between thyroid dimensions and fetal growth parameters. The strongest correlations were noted between CRL and right lobe length (r=0.990), left lobe length (r=0.986), and right lobe thickness (r=0.982) (p<0.001). Thyroid weight also showed strong correlations with right lobe thickness (r=0.980) and right lobe length (r=0.976). Conclusion: The fetal thyroid gland exhibits progressive enlargement with advancing gestation and demonstrates strong associations with overall fetal growth, particularly CRL. These findings provide valuable baseline morphometric data for developmental anatomy, fetal pathology, prenatal imaging, and assessment of fetal thyroid development.

Keywords: Fetal thyroid gland, morphometry, gestational age, crown-rump length, fetal growth.