Abstract
<title>Abstract</title> <p>Background Accurate assessment of gestational age and early detection of fetal developmental abnormalities are essential components of prenatal care. Transcerebellar diameter (TCD) has emerged as a promising ultrasonographic parameter due to its strong association with gestational age and relative resistance to growth disturbances. Methods This retrospective cross-sectional diagnostic study included 400 singleton pregnancies evaluated at two tertiary referral centers in Qom, Iran. Gestational age was confirmed using first-trimester crown–rump length measurements. Fetal biometric parameters, including TCD, biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL), were extracted from archived ultrasound records. Pearson correlation, linear regression, Bland–Altman agreement analysis, and receiver operating characteristic (ROC) curve analysis were performed to assess the predictive and diagnostic performance of TCD. Results TCD demonstrated a strong positive correlation with gestational age (r = 0.930, P < 0.001). Linear regression analysis showed that TCD explained 86.5% of gestational age variability (R² = 0.865). Bland–Altman analysis revealed acceptable agreement between actual and TCD-estimated gestational age (mean difference: 0.002 ± 2.03 weeks). Among all biometric parameters, TCD was the only measurement significantly lower in fetuses with developmental abnormalities compared with normal fetuses (22.75 ± 5.04 vs. 27.47 ± 5.62 mm, P < 0.001). ROC analysis yielded an AUC of 0.729 (95% CI: 0.669–0.788), with a cutoff value of 25.95 mm providing 73.3% sensitivity and 60.0% specificity. Conclusion TCD is a reliable parameter for gestational age estimation and demonstrates moderate diagnostic accuracy for identifying fetal developmental abnormalities. Its incorporation into routine fetal biometry may enhance prenatal assessment and improve the detection of abnormal fetal development.</p>