Accuracy of Sonographic Modules in the Estimation of Birth Weight: An Analytical Study of Antenatal Women in Enugu, Nigeria

Abstract

Introduction: Antenatal sonographic estimation of foetal weight is a common practice. The use of these estimates to predict actual birth weight is crucial for appropriate management of certain pregnancy conditions, to improve fetomaternal outcome. Aim: To evaluate the accuracy of foetal weights derived from six selected sonographic modules, in estimating the actual birth weight of neonates in Enugu, Nigeria. Materials and Methods: This was a cross-sectional, analytical study of 245 consenting consecutive antenatal women with term singleton pregnancies at the UNTH, Enugu, Nigeria, from October 2013 to May 2014. For the Estimated Foetal Weights (EFW), foetal parameters obtained after obstetric ultrasound scan of each participant were keyed into the sonographic modules. Actual Birth Weight (ABW) and Scan Delivery Interval (SDI) were obtained after delivery. Accuracy of the sonographic modules in estimating the ABWs was determined using percentage (%) error, the proportion of EFW within 10% of ABW, sensitivity/ specificity tests, and ROC curve analysis. Results: The Hadlock Biparietal Diameter (BPD)/Abdominal Circumference (AC)/Femur Length (FL) and Hadlock BPD/AC modules had the least systematic error (-0.5% and -0.7% respectively) compared to other modules, and higher proportions of accurate estimated foetal weight within 10% of actual birth weights (78% versus 78.4%). For new-borns in the normal weight category, Hadlock BPD/AC module best predicted the ABW (ROC curve area=0.737, p=0.006). Conclusion: The Hadlock BPD/AC formula consistently showed a high accuracy for estimation of foetal weight. It is comparable with Hadlock BPD/AC/FL module but, has an advantage of requiring fewer foetal parameters.

Keywords

• foetal weight
• prenatal
• sensitivity
• specificity
• ultrasonography