Previous prognostic studies of infants with intrauterine growth retardation (IUGR) have not adequately considered the heterogeneity of IUGR in terms of cause, severity, and body proportionality and have been prone to misclassification of IUGR because of errors in estimation of gestational age. Based on a cohort of 8719 infants with early-ultrasound-validated gestational ages and indexes of body proportionality standardized for birth weight, the consequences of severity and cause-specific IUGR and proportionality for fetal and neonatal morbidity and mortality were assessed. With progressive severity of IUGR, there were significant (all P < .001) linear trends for increasing risks of stillbirth, fetal distress (abnormal electronic fetal heart tracings) during parturition, neonatal hypoglycemia (minimum plasma glucose <40 mg/dL), hypocalcemia (minimum Ca <7 mg/dL), polycythemia (maximum capillary hemoglobin ≥21 g/dL), severe depression at birth (manual ventilation >3 minutes), 1-minute and 5-minute Apgar scores ≤6, 1-minute Apgar score ≤3, and in-hospital death. These trends persisted for the more common outcomes even after restriction to term (37 to 42 weeks) births. There was no convincing evidence that outcome among infants with a given degree of growth retardation varied as a function of cause of that growth retardation. Among infants with IUGR, increased length-for-weight had significant crude associations with hypoglycemia and polycythemia, but these associations disappeared after adjustment for severity of growth retardation and gestational age. Increased length-for-weight and head circumference-for-weight, however, were associated with slightly increased risks of stillbirth and fetal distress, respectively, even after adjustment. It is concluded that IUGR, especially when severe and regardless of cause, is an important determinant of numerous adverse metabolic and asphyxic fetal and neonatal outcomes. Disproportionality is a proxy for severe IUGR and carries little or no additional risk.

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