Big baby, birth defects caused by diabetes? What defines macrosomia?

Not just big. Fetal macrosomia can be suspected by serial ultrasound in which the fetus exceeds the 90th percentile. This means that the baby is larger than 89% of the babies of same gestational age. Furthermore"macrocosmic" fetus are at a higher risk of shoulder dystocia (difficulty of delivering shoulders after the head is out) and hypoglycemia or dropping blood sugars shortly after delivery.