Fetal weight estimation in diabetic pregnancies and suspected fetal macrosomia

To review the literature on the accuracy of sonographic estimated fetal weight (EFW) in diabetic pregnancies, specifically on its role in the prediction and clinical management of fetal macrosomia.

An English language literature search of Medline listings was performed to review the recently published data on sonographic fetal weight estimation in diabetic pregnancies and suspected fetal macrosomia.

Ultrasound biometry used to detect macrosomia is characterized by low sensitivity, low positive predictive value, and high negative predictive value. Serial sonographic measurements and the use of additional examiners can increase the positive predictive value. Regardless of the formula used, the accuracy of the sonographic estimate decreases with increasing birth weight. Three-dimensional ultrasound and magnetic resonance imaging techniques are still investigational. To date, none of the management algorithms developed for selective interventions that are based on the sonographic EFW have demonstrated any efficacy in reducing the incidence of either shoulder dystocia or brachial plexus injury.

The true value of ultrasonography in the management of fetal macrosomia may be its ability to rule out the diagnosis. Ultrasound-derived fetal weight estimates alone are not sufficient grounds for deciding the route of delivery. To assess the risk of macrosomia, other known risk factors should also be taken into account. To determine the mode of delivery, the clinical fetal weight estimate, subjective maternal weight estimate, and clinical assessment of pelvic capacity should be added to the sonographic fetal weight estimate, with consideration of the risk factors for macrosomia.