The macrosomic fetus: a challenge in current obstetrics

Although the causes of high birthweight include both genetic and environmental factors, the rapid increase in the prevalence of large newborns has environmental causes. The evidence is extensive that maternal overweight and associated metabolic changes, including type 2 and gestational diabetes, play a central role. There is a paucity of studies of the effect of intervention before and/or during pregnancy on the risk of having an 'overweight newborn'. It appears rational, however, that preventive measures should primarily be implemented before pregnancy and should include guidance about nutrition and physical activity in order to reduce the prevalence of overweight. In pregnancy, limited weight gain, especially in obese women, seems to reduce the risk of macrosomia, as do good control of plasma glucose among those with diabetes. Prediction of fetal macrosomia remains an inaccurate task even with modern ultrasound equipment. There is little evidence that routine elective delivery (induction or caesarean section) for the mere reason of suspected macrosomia should be employed in a general population. Vaginal delivery of a macrosomic fetus requires considered attention by an experienced obstetrician and preparedness for operative delivery, shoulder dystocia and newborn asphyxia.