Accuracy of clinical and ultrasound estimation of fetal weight in predicting actual birth weight in Enugu, Southeastern Nigeria

Abstract

Background: Estimation of fetal weight is important for antenatal and intrapartum management of pregnant women. Sonographic methods are not readily accessible in under.resourced settings, it is therefore necessary to study the accuracy of a clinical method of estimating fetal weight where this limitation (unavailability of ultrasound) exists.
Objective: To compare the accuracy of clinical and ultrasound methods of fetal weight estimation at term.
Materials and Methods: Clinical and ultrasound fetal weights were  estimated on 200 consecutive term pregnancies (37 completed weeks of gestation . 41 weeks and 6 days) at the University of Nigeria Teaching  Hospital, Enugu, Nigeria from 1st April to 30th November 2012. Accuracy was determined using percentage error, absolute percentage error, and proportion of estimates within 10% of actual birth weight.
Results: Actual birth weight had strong positive correlation with both clinical and ultrasound estimated fetal weights (r = 0.71, P < 0.001 and r = 0.69, P < 0.001, respectively). Overall, both the clinical and ultrasound methods systematically overestimated the actual birth weight. The proportion of the clinical estimated weights that were within 10% of the actual birth weight was significantly lower than that of ultrasound method for babies of all birth weights (35.0 vs. 67.5%; P < 0.001) and for macrosomic babies (76 vs 100%, P = 0.009). For babies with normal birth weights (2.5-3.9 kg), ultrasound method error values were significantly lower than those of  clinical method for both the mean % error (5.4 vs 19.6%; P < 0.001) and the mean absolute % error (9.97 vs 20.6%; P < 0.001).
Conclusion: The ultrasound method is generally a better predictor of the actual birth weight than the clinical method, and thus should be used in estimating the actual birth weight when accessible.

Key words: Birth weight, clinical estimation, Nigeria, ultrasound estimation