Increased neonatal urinary ammonia: a marker for in utero caloric deprivation?

The decline in the urinary urea to ammonia ratio represents a simple measure of nutritional status in the adult. We examined the relationship of this ratio to nutrient-related fetal growth retardation. Levels of ammonia and urea nitrogen were measured in the first voided urine and cord blood from 15 term infants exhibiting a wide range of growth. Analysis by multiple regression with neonatal ponderal index as the primary dependent variable revealed a significant correlation between lowered ponderal index and decreased urinary urea and ammonia. The correlation was primarily a function of increasing ammonia levels, with no relationship between fetal leanness and urinary urea. Comparable cord artery and vein ammonia suggest that placental ammoniagenesis was not a major determinant of observed elevations in urinary ammonia. Confirmation of the striking correlation between increased urinary ammonia and lowered neonatal ponderal index may afford a simple test for the identification of nutrient-related growth retardation.