Fetal weight estimation in diabetic pregnancies: The real facts

Ultrasound plays a crucial role in the management of diabetic pregnancies. Among its aims is the correct estimation of fetal weight, especially when suspicion of either macrosomia or IUGR develops during pregnancy. Although ultrasound can detect in many instances the macrosomic fetus, still a debate exists regarding the use of EFW in preventing adverse outcome. A macrosomic fetus may be defined as one whose absolute weight is of 4000-4500 grams and in the diabetic patient the macrosomia is asymmetric (AC>HC), leading to an increased risk of shoulder dystocia. Therefore, US prediction of fetal weight in extremely important.
The question to be asked is: is US a goof tool for EFW in utero!'' Several methods for EFW exist: clinical, maternal, sonographic (2D, 3D) and by MRI. Over the last 30 years, numerous formulas for EFW have been suggested using sonographic measurements of fetal organs with consideration of AF1 and obesity. The predictive accuracy of these formulas varies from +/- 14.8% to +/- 20.2%, and the accuracy is related to the size of the fetus. It was found by many investigators that formulas incorporating AC alone are better than those using measurements of BPD. Regardless of the formula used, the accuracy of the FFW decreases with increasing BW. In most recent published articles it was found that only 50-100% (median 62%) of macrosomic fetuses are successfully predicted by sonographic measurements, and 15-81% (median 67%) predicted to be macrosomic are confirmed to be macrosomic at birth.
3D US may help assessing fetal BW offering some superiority to standard 2D techniques, but we have to wait for results of studies in progress attempting to establish its clinical relevance in the practice of obstetrics.
In conclusion, it was found that sonographic estimated are no more accurate than clinical estimates of fetal weight. Regardless of method used - the higher the actual BW, the less accurate the BW prediction. To date, no management algorithm involving selective interventions based on El-'W, demonstrated efficacy in reducing the incidence of either shoulder dystocia or brachial plexus injury.