Validation of a birth weight prediction equation based on maternal characteristics.

Objective: To validate the accuracy of a birth weight prediction equation based on maternal and pregnancy-specific characteristics and to assess its value in predicting fetal macrosomia.

Study Design: A previously published birth weight prediction equation based on maternal and pregnancy-specific characteristics was used to predict birth weight in 244 Caucasian gravidas with uncomplicated, singleton, term pregnancies. Results were assessed by calculating the mean absolute error, the mean absolute percentage error and the percentage of birth weights correctly predicted to within +/- 10% and +/- 15% of actual birth weight. The sensitivity, specificity and positive and negative predictive value for predicting fetal weight > 4,000 g were calculated.

Results: Birth weight was accurately predicted to within an average of +/- 8.1% (+/- 280 g). The percentage of weights accurately predicted to within 15% of actual birth weight was 87%, and the percentage predicted to within +/- 10% was 68%. The sensitivity for predicting fetal weight > 4,000 g was 52%, specificity 90%, positive predictive value 42% and negative predictive value 93%. The area under the receiver operating characteristic curve for predicting fetal macrosomia was 0.83.

Conclusion: An equation using maternal and pregnancy-specific characteristics can predict term birth weight in gravidas with uncomplicated singleton pregnancies to within +/- 8.1% (+/- 280 g). The accuracy of the method for predicting birth weight > 4,000 g is comparable to that obtained using ultrasonic fetal biometry.