Small for gestational age (birth weight below 10th percentile)
Symmetric
	Features: onset early in gestation; brain size corresponding with body size; glycogen and fat content corresponding with body size (hence, lower risk of hypoglycemia)
	Etiology: environmental factors such as smoking or drugs (heroin, methadone, ethanol, phenytoin [Dilantin]); genetic factors such as small maternal size or chromosomal disorder (trisomy 13, 18, and 21 syndromes, Turner's syndrome); intrauterine infections such as TORCH, bacterial (tuberculosis), or spirochetic (syphilis); metabolic disorders such as phenylketonuria
Asymmetric
	Features: onset late in gestation; no effect or minimal effect on fetal brain growth; reduced glycogen and fat content relative to body size (hence, increased risk of hypoglycemia); increased risk of perinatal asphyxia and polycythemia (hyperviscosity)
	Etiology: uteroplacental insufficiency with chronic fetal hypoxia
Large for gestational age (birth weight above 90th percentile)
Features: increased incidence of perinatal asphyxia and birth injuries; respiratory distress syndrome; hypoglycemia
Etiology: maternal diabetes (increased likelihood of large birth size, respiratory distress syndrome, and hypoglycemia)