Predictive Accuracy of Foetal Trascerebellar Diameter in Gestational Age Estimation with Foetal Cerebellar Grading

Abstract

Introduction: Determination of gestational age is important in obstetrics for management of pregnancy and evaluation of foetal development. An error in the gestational age estimation results in prematurity and post maturity and, if expected date of delivery is not known, higher perinatal mortality is the obvious outcome. Aim: To evaluate accuracy of transcerebellar diameter in gestational age estimation, to determine the ratio between transcerebellar diameter and abdominal circumference as a gestational age independent parameter, and to study the change in ultrasonographic appearance of the foetal cerebellum with advancing gestation and its grading. Materials and Methods: In 100 normal singleton pregnant women between 15 to 37 weeks of gestation, Biparietal Diameter (BPD), Head Circumference (HC), Abdominal circumference (AC) and Femur Length (FL) and Transcerebellar Diameter (TCD) were measured for assessing the sonological gestational age. TCD/AC ratio was also calculated and simultaneously, the ultrasonographic appearance of the foetal cerebella with advancing gestation were noted and grouped into three grades. Results: In the present study, statistically significant linear relationship between TCD and gestational age in normal pregnancies was noted. TCD measured in millimeters was almost equal to gestational age up to 23 weeks. The TCD/AC ratio remained fairly constant throughout gestational age with a mean ± SD of 13.76 ± 0.77. As with advancing gestation, foetal cerebellum showed a gradual change in US appearance of the progressing from Grade I to Grade III. Conclusion: Correlation and regression analysis indicated a good correlation of TCD with gestational age and other. Hence, TCD can be used as a single growth parameter to predict the gestational age in cases where LMP (Last Menstrual Period) is uncertain. TCD/AC ratio can be used as a good tool to diagnose asymmetric Intra Uterine Growth Retardation (IUGR) in those with ratio exceeding 2 SDs as it is gestational age independent factor which remained fairly constant throughout gestation. We observed a gradual and progressive change in ultrasound appearance of foetal cerebellum from Grade 1 to Grade 3 with advancing gestation.

Keywords

• biparietal diameter
• cerebellum
• foetal biometry
• ultrasound