A computerized method for accurately predicting fetal macrosomia up to 11 weeks before delivery.

Objective: To improve the prediction of birth weight and fetal macrosomia by combining sonographically derived fetal biometric data with routinely recorded pregnancy-specific information.

Study Design: Retrospective data were obtained for 218 normal gravidas who had obstetrical ultrasonography performed within 11 weeks of delivery. Multiple regression was employed to derive a set of equations for predicting birth weight that used different combinations of ultrasonographic and pregnancy-specific variables.

Results: A set of 38 unique combination equations was derived to accurately predict birth weight up to 11 weeks before delivery. The equations use different combinations of ultrasonographic and pregnancy-specific variables, so that predictions are still possible in the face of missing data. When ultrasonographic measurements are taken within 3 weeks of delivery, fetal macrosomia is predicted with 75% sensitivity, 93% specificity, and 67% and 95% positive and negative predictive value, respectively. The equations are equally as accurate for primiparous and multiparous women from all racial groups. A jackknifing procedure was used to validate the predictive accuracy of the equations for use with new subjects.

Conclusion: The combined approach of predicting fetal macrosomia using ultrasonographic fetal measurements and pregnancy-specific characteristics is superior to pre-existing approaches that rely on either method alone. The method can be used up to 11 weeks before delivery, allowing fetal macrosomia to be predicted reliably in low-risk populations sufficiently early for prospective clinical intervention to be undertaken.