Estimation of Gestational Age According to Crown-Rump Length in Nepalese Population: A Comparison with Previously Published Nomograms

Background/Objective: This study was performed to construct an institution specific crownrump length (CRL) nomogram and to compare its ability to predict gestational age with previously published nomograms. Patients and Methods: A regression model was developed for estimation of gestational age using CRL measurements of 123 singleton fetuses in the Nepalese population. Measurements were obtained by placing the calipers of the ultrasound machine from the crown to the rump. The appropriateness of previously established CRL nomograms for predicting the gestational age was assessed in the Nepalese population to determine comparability between nomograms. Results: CRL corresponds to Robinson's nomogram up to 9 weeks of gestational age. There is a deficiency of 2mm at 10 weeks, 5 mm at 11 weeks and 8 mm at 12 weeks. Conclusion: CRL measurements are used as a reliable method for estimation of the gestational age as well as a baseline for comparing gestational ages later. CRL corresponds to Robinson's nomogram up to 9 weeks gestational age. There is a deficiency of 2-8 mm from 10-12 weeks gestational age. Difference with the established nomograms may be due to ethnic differences of the fetal development. After 12 weeks, CRL measurement is unreliable due to flexion of the fetus.