Infants whose weight is > the 90th percentile for gestational age are classified as large for gestational age (LGA). The predominant cause is maternal diabetes. Complications include birth trauma, hypoglycemia, and hyperbilirubinemia.

Other than genetically determined size, the major cause of an infant's being LGA is maternal diabetes mellitus. The macrosomia results from the anabolic effects of high fetal insulin levels produced in response to excessive blood glucose during gestation. The less well controlled the mother's diabetes during pregnancy, the more severe is the fetal macrosomia.A rare nongenetic cause of macrosomia is Beckwith-Wiedemann syndrome (characterized by macrosomia, omphalocele, macroglossia, and hypoglycemia).

Symptoms, Signs, and Treatment

LGA infants are large, obese, and plethoric. These infants are often listless and limp and may feed poorly. Delivery complications can occur in any LGA infant. Metabolic and respiratory complications are specific to LGA infants of diabetic mothers.

Delivery complications: Because of the infant's large size, vaginal delivery may be difficult and occasionally results in birth injury. Shoulder dystocia, fractures of the clavicles or limbs, and perinatal asphyxia may occur. Therefore, cesarean section should be considered when the fetus is thought to be LGA, especially if the mother's pelvic measurements are at the lower end of normal.

Infants of diabetic mothers: These infants are very likely to become hypoglycemic in the first 1 to 2 h after delivery because of the state of hyperinsulinism and the sudden termination of maternal glucose when the umbilical cord is cut. Neonatal hypoglycemia can be prevented by close prenatal control of the mother's diabetes and by the prophylactic IV infusion of 10% dextrose in water into the infant until early frequent feedings can be established. Blood glucose levels should be closely monitored by bedside testing during the transition period.

Hyperbilirubinemia (see also Metabolic, Electrolyte, and Toxic Disorders in Neonates: Neonatal Hyperbilirubinemia) is common because of intolerance for oral feedings in the earliest days of life, which increases the enterohepatic circulation of bilirubin. Hyperbilirubinemia can also result from the infant's high Hct (another accompanying problem in infants of diabetic mothers).

Because surfactant production (and hence pulmonary maturation) may be delayed until late in gestation, respiratory distress syndrome may develop even if the infant is delivered only a few weeks prematurely. The lecithin/sphingomyelin ratio, and especially the presence of phosphatidyl glycerol, in amniotic fluid obtained by amniocentesis can evaluate fetal lung maturity and help determine the optimal time for safe delivery. Lung maturity can be assumed only if phosphatidyl glycerol is present. Treatment is discussed elsewhere (see Respiratory Disorders in Neonates, Infants, and Young Children: Treatment).

Last full review/revision March 2007 by James W. Kendig, MD

Content last modified February 2012