Urinary urea-nitrogen ratio as an index of protein nutrition in diabetic pregnancy.

Urinary urea nitrogen-total nitrogen ratio (UN/TN) was measured at intervals throughout pregnancy in 12 normal women and in 10 with insulin-dependent diabetes mellitus and the results were related to protein ingestion estimated by dietary history. While urea and nitrogen correlated significantly with each other in both normal and diabetic subjects, the relationship between UN/TN and protein intake was quite different in the two groups. Nondiabetic patients exhibited generally close correlation between UN/TN and protein intake with statistically significant correlation coefficients (r = 0.74-0.99) in 11 of 12 subjects. In none of the 10 diabetic patients, however, was significant correlation found. While the reliability of the index in diabetic patients tended to improve as hyperglycemia lessened, even under conditions considered clinically to indicate excellent metabolic control (mean plasma glucose less than or equal to 125 mg/dl), UN/TN still did not correlate significantly with protein intake. These observations suggest that the unstable carbohydrate metabolism characteristic of diabetes mellitus may be responsible for altered protein retention during pregnancy. From a clinical point of view, the utility of urinary urea studies as a simple and objective index of protein intake in the normal pregnant women does not apply in the diabetic patients.