Utility of sonographic transcerebellar diameter in the assessment of gestational age in normal and intrauterine growth-retarded fetuses.

BACKGROUND: The fetal cerebellum has been shown to be least affected by external pressures and molding during pregnancy and therefore might provide more accurate estimation of GA. AIMS: To study the utility of transcerebellar diameter (TCD) measured by ultrasound for the detection of GA in normal and intrauterine growth-retarded (IUGR) fetuses. SUBJECTS AND METHODS: This cross-sectional study comprised 500 antenatal patients with a GA between 14 and 39 weeks and who were certain of their last menstrual periods. The TCD was measured ultrasonographically and the corresponding GA was determined. The GA was also determined with other customarily used sonographic parameters such as biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL) and compared with TCD. Data of normal pregnancy patients was used to formulate nomograms by taking the 5th, 50th, and 95th percentile measurements. TCD to AC ratio was also calculated in both normal (n = 424) and IUGR pregnancies (n = 76). RESULTS: TCD showed significant correlation with gestational age (GA) measured by last menstrual period (LMP) as well as with GA calculated with other biometric fetal parameters. TCD also showed significant correlation with GA in normal (R2 = 0.979) as well as with IUGR pregnancies (R2 = 0.942). TCD to AC ratio remained fairly constant in normal pregnancies while it was increased in IUGR pregnancies. CONCLUSIONS: TCD and TCD/AC ratio can be employed as an objective parameter to establish the GA in normal as well as IUGR pregnancy cases.