Sonographic Correlation between Distal Femoral Epiphysis Ossification Centre Diameter and Gestational Age in the Third Trimester of Pregnancy: A Prospective Cohort Study

Background: Accurately determining gestational age during the third trimester is crucial for appropriate prenatal care. As seen on sonograms, the ossification center of the distal femoral epiphysis could serve as a dependable marker for this purpose. Objective: This study aimed to correlate the sonographic distal femoral epiphysis ossification center diameter (DFOC) and the gestational age calculated by crown rump length (CRL) in the period between 28 weeks and 40 weeks gestation Methods: A prospective observational study included 74 women in their third trimester of pregnancy. The study was conducted at Badr University Hospital, Helwan University, from January 2024 to June 2024. Our Primary outcome was the correlation between DFOC and gestational age and its diagnostic accuracy in the prediction of Gestational age. In contrast, the Secondary Outcome was Ultrasound biometry of studied cases (BPD, AC, HC, and FL). Results: The findings showed a significant correlation between the diameter of the distal femoral epiphysis ossification center and gestational age in the third trimester. At 32 weeks of gestation, the distal femoral epiphysis has a sensitivity of 68.2% and a specificity of 67.5%. Its positive predictive value (PPV) is 95.13%, and its negative predictive value (NPV) is 18.5%. The overall accuracy of the indicator at 32 weeks is 72.4%. At 36 weeks of gestation, the sensitivity increased to 98.3%, and the specificity increased to 82.7%. The positive predictive value was 97.6%, and the negative predictive value was 81.0%. The accuracy of the distal femoral epiphysis as an indicator of gestational age at 36 weeks was 96.9%. Conclusion: As measured by ultrasound, the diameter of the ossification center in the distal femoral epiphysis seems to be a potential non-invasive approach for estimating gestational age during the third trimester.