Actual Birth Weight Prediction at Term Using Clinical and Ultrasound Methods at Federal Medical Centre, Keffi, Nasarawa State: A Comparative Approach

Objective: The study sought to compare the predictive accuracy of clinical and ultrasound fetal weight estimation in predicting the actual birth weight of pregnant women at term at the FMC, Keffi, North central Nigeria.

Materials and Methods: This study was a cross-sectional study that enrolled 360 consecutive pregnant women at term (37 weeks + 0day - 41weeks +6days), who met the inclusion criteria between 10th December 2018 to 25th July 2019. Informed consent was obtained from participants and a proforma was interviewer-administered. The clinical estimate was done using the Dare’s formula in the lying- in ward and labour ward. The ultrasound fetal weight estimation was done using an ultrasound scan machine imputed with the Hadlock formula mode (BPD, HC, AC, and FL) while the actual birth weight was measured in the labour room using the infant weighing scale. The data collected were analyzed using the Pearson’s Chi- square or Fisher’s exact test as appropriate, Pearson’s correlation analysis and student’s t test. Accuracy was determined using percentage error, absolute error, and proportion of estimates within 10% of actual birth weight; and compared using the Poisson’s z-test for two proportions. All analyses were performed, using the IBM SPSS Statistics for Windows, version 20.0. (IBM Corp., Armonk, N.Y., USA) and Minitab, version 18.

Results: Analysis showed that the clinical fetal weight estimation within 10% of the actual birth weight was not significantly lower than that of ultrasound fetal weight estimation for babies of all birth weight ( 41.5% vs. 55.0%, P = 0.064). The actual birth weight had a strong correlation with both clinical and ultrasound fetal weight estimation (r = 0.53, P <0.001 and r = 0.55, P < 0.001 respectively). The mean percentage error and mean absolute percentage error for normal weight babies (2.5- 3.99kg) was significantly higher in clinical method than ultrasound method (-13.29kg vs. 4.49 kg, P< 0.001) and (14.14kg vs. 9.47 kg, P< 0.001) respectively. Overall in most cases, the clinical method of fetal weight estimation overestimated the actual birth weight.

Conclusion: It was concluded that, ultrasound method of fetal weight estimation is a better predictor of actual birth weight than the clinical method. However, clinical weight estimation can still be used in a low-resource setting such as ours