At the other end of the spectrum of fetal growth abnormalities are newborns who are large-for-gestational-age (LGA) infants. LGA infants may have associated metabolic abnormalities (hypoglycemia, hypocalcemia), traumatic birth injuries, polycythemia, hyperviscosity, and hyperbilirubinemia, as well as the possibility of various congenital anomalies. Newborns are considered to be LGA if they weigh more than the 90th percentile for their gestational age or if they weigh more than 4000 g (8 lb 13 oz). Macrosomia is a clinical term describing excessive weight for gestational age; it results from increased adiposity caused by adipocyte hyperplasia and hypertrophy. Infants whose birth weight exceeds the 97th percentile (>4500 g, 9 lb 4 oz) are at greater risk for neonatal morbidity, with babies weighing more than 5000 g (11 lb) at highest risk for death.[5] A subpopulation of LGA infants born to mothers with diabetes mellitus (before or during pregnancy) has various abnormalities. These infants are labeled under a syndrome known as infant of diabetic mother (IDM). Some of the IDMs born to mothers with long-standing diabetes mellitus and vascular disease may be SGA.

LGA infants can result from being born to obese mothers (constitutional), from gestations longer than 42 weeks (postmaturity), or as the result of overstimulation of growth in utero. Additional risk factors include maternal weight gain during pregnancy, multiparity, a male fetus, and ethnicity. Infants of mothers with pregestational diabetes mellitus or gestational diabetes are exposed to high blood sugar during fetal development, or they may develop high circulating insulin levels and may therefore grow excessively. Women with gestational diabetes with glucose tolerance during late pregnancy (a positive glucose challenge test with a negative glucose tolerance test) may remain undiagnosed and may deliver a macrosomic infant with greater perinatal complications. Infants with Beckwith-Wiedemann syndrome and other genetic disorders that result in early excessive fetal growth, as well as infants with erythroblastosis fetalis, may exhibit as LGA with or without hyperinsulinism.