Accuracy of Transverse Cerebellar Diameter in Estimating Gestational Age in the Second and Third Trimester: A Prospective Study in Saudi Arabia

<b>Background:</b> Failure to accurately estimate gestational age remains an important dilemma for optimal evidence-based antenatal care. Currently, when the last menstrual period (LMP) is unknown, ultrasonography measurement is the best method for estimating gestational age (GA). This study aims to assess the feasibility and accuracy of ultrasonography measurement of the transverse cerebellar diameter (TCD) to deduce fetal GA after 13 weeks of gestation. <b>Methods:</b> A prospective study was conducted on 384 normal singleton pregnancies. Demographic information and biometric measurements, including TCD, were collected using a data sheet. The data were then analyzed using SPSS version 27, DATAtab, and the R program. <b>Results:</b> The study found a strong significant association between GA based on TCD and the LMP, GA based on femur length (FL), GA based on biparietal diameter (BPD), GA based on abdominal circumference (AC), and GA based on the average gestational age (AVG) (r = 0.976, 0.970, 0.966, 0.968, and 0.984, respectively, <i>p</i> < 0.001). Furthermore, there was perfect agreement between GA estimated using TCD and GA based on LMP, with a mean difference of 0.41 weeks and upper and lower limits of agreement of -1.43 to 2.26 weeks. <b>Conclusions:</b> Ultrasonography measurements of the TCD accurately predict gestational age with excellent concordance with GA based on the LMP, FL, AC, and BPD. TCD can be used as a reliable estimator of GA in the second and third trimesters of pregnancy with the benefit of its brain-sparing effect in fetuses of fetal intrauterine growth restriction pregnancies. Combining TCD with FL, BPD, and AC provides the most accurate method of GA prediction.