Introduction: Gestational age estimation is of prime importance in anticipating the day of delivery and preventing obstetric complications. Several ultrasonogram measured foetal parameters arc used to determine gestational age which include crown -rump length (CRL), biparietal diameter (BPD), head circumference (HC), femur length (FL), abdominal circumference (AC) and trans-cerebellar diameter (TCD). TCD and FL have been proposed as variables which are not subjected to much variation due to intra-uterine forces other than growth of the foetus.

Materials and Methods: A hospital-based, prospective study was conducted in the Department of Radiology, Andhra Medical College, Visakhapatnam between October 2018 and February 2020 on 100 normal singleton pregnant women with normal foetal growth pattern.

Results: The study showed that the study participants were mostly young women (mean age= 25.6±4.53) with majority in the 21-25 years age group (74%) and primigravida (61%). The gestational age as determined by CRL in first trimester correlated significantly [p<0.001] with the TCD (mm) values (r² = 0.9545) and FL (mm) values (r² = 0.975) measured in the third trimester. TCD and FL showed significant [p<0.001] positive correlation (r² = 0.870) in determining GA. The reliability of the two parameters in assessing gestational age was 87% and a percentage error of 0.082%.

Conclusion: The study established the TCD and FL values in third trimester of pregnancy among normal singleton pregnant women. It also showed there was significant correlation of the TCD and FL values measured in third trimester with gestational age determined by CRL in the first trimester. Hence TCD and FL can both be used as reliable and individually used intra-uterine foetal biometric parameters in estimating the gestational age during the third trimester of a normal pregnancy.

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Dr S. Vandana Sasi Kiran MD (RD)

Assistant Professor, Department of Radio-Diagnosis, Andhra Medical College, Visakhapatnam, India