Fetal Transcerebellar Diameter in Estimating Gestational Age in Third Trimester of Pregnancy
Background: Accurate determination of gestational age (GA) is of critical importance, it can positively affect pregnancy outcomes. In the third trimester, the reliability of any single ultrasound parameter in gestational age determination is poor. Fetal transcerebellar diameter (TCD) can help as an alternative parameter to the most frequently used biometric parameters to date pregnancy.
Aim: To evaluate the accuracy of fetal transcerebellar diameter (TCD) in estimating gestational age at the third trimester of pregnancy using the last menstrual period (LMP) as a reference for the actual period of gestation.
Materials and methods: In this descriptive study, a total of 65 pregnant women with uncomplicated pregnancies between 28 to 40 weeks of gestation with known LMP were enrolled. Ultrasonographic measurement of fetal TCD was done along with routine parameters. TCD was measured by identifying the cerebellum in the posterior fossa and measuring the transcerebellar distance from the outer edge to the outer edge. Gestational age using TCD was calculated and compared with estimated gestational age based on LMP.
Results: Statistical analysis showed a strong and significant correlation between the estimated gestational age by LMP and each of biparietal diameter (BPD), femur length (FL), and TCD; the latter having the highest correlation coefficient (r=0.931, p=0.0001; r=0.931, p=0.0001 r=0.955, p=0.0001; respectively). Even when considering fetal sex whether male or female, the TCD was the best parameter to correlate with gestational age by LMP.
Conclusion: Fetal transcerebellar diameter can be taken as a good indicator of gestational age in late pregnancy.