Publication:

Sonographic estimation of foetal weight versus actual birth weight at term

Background Estimated foetal weight is very critical to decision making in the management of pregnant women. It is therefore important to evaluate the accuracy of ultrasound estimated foetal weight (USEFW) at term in our environment. We compared ultrasound estimated foetal weight at term with the actual foetal birth weight at delivery.

Methods This was a prospective, comparative cross-sectional study at the Lagos State University Teaching Hospital over a 6-month period. Four hundred and five pregnant women with normal singleton pregnancy, who had sonographic estimation of foetal weight at term, using the Hadlock IV formula, were followed up and had their actual birth weight (ABW) determined at delivery. Accuracy was determined by proportion of estimates within 10% of actual birth weight and mean absolute percentage error (MAPE). The p<0.05 was considered significant at 95% confidence interval.

Results The prevalence of macrosomia was 10.3%. At 10% margin of error, ultrasound accurately estimated the weights of 73.3% of babies. The mean USEFW was 3559.89±316.9g and mean ABW was 3477.42±422.9g with a mean difference of 82.44g (p<0.001) and MAPE of 7.11. There was positive correlation (r=0.669) between the EFW and ABW (p<0.001). The USEFW had a sensitivity of 66.7%, specificity of 91.5%, positive predictive value of 47.5% and negative predictive value of 96.0% in predicting macrosomia.

Conclusions Ultrasound estimation of foetal weight at term is reliably accurate in predicting actual birth weight in south-western Nigeria.