Neonatal morphometrics and perinatal outcome: who is growth retarded?

To evaluate the relationship between neonatal morphometrics and poor neonatal outcome resulting from fetal malnutrition, we prospectively examined 355 sequential live-born, singleton neonates greater than 35 weeks' gestational age. Birth weight, neonatal ponderal index, and midarm circumference to head circumference ratio were measured. A birth weight, ponderal index, or midarm circumference to head circumference ratio less than or equal to tenth or greater than or equal to ninetieth percentiles for gestational age was considered abnormal. Poor outcome was defined as operative delivery for fetal distress, 5-minute Apgar score less than 7, meconium aspiration, polycythemia, or hypoglycemia. Thirty-three (9.3%) neonates had perinatal morbidity. Although morbidity was not increased among neonates that were large by any of the criteria, five (25%) of 20 with low birth weight had poor outcome and 18 (26%) of 70 with low ponderal index or midarm circumference to head circumference ratio suffered morbidity. Of the 33 neonates with morbidity, 18 (54.5%) had low ponderal index or midarm circumference to head circumference ratio, but only five (15.2%) had low birth weight. Therefore, low ponderal index and midarm circumference to head circumference ratio are more sensitive predictors of outcome than is birth weight. As such, ponderal index and midarm circumference to head circumference ratio are more appropriate end points for antenatal diagnostic studies than is birth weight.