Nitrogen Retention, Total Body 40K and Weight Gain in Teenage Pregnant Girls

Abstract

Nitrogen (N) retention was measured in 10 primigravid women, 15 to 19 years of age, during the third trimester, by balance technique. The subjects were fed nutritionally adequate, natural food diets for several 12-day periods. Urinary creatinine excretion was used as a parameter of lean body mass in order to relate N intake to lean body size. Total N intake ranged from 9.3 to 20.0 g per day, with 90% from animal sources. Nitrogen balance was positive over all levels studied, varied from 0.31 to 6.50 g per day, and correlated highly with N intake. Nitrogen retention values were documented by appropriate weight gain and potassium (K) deposition. As measured by total body ⁴⁰K counts, K accretion was 3.4 mEq per day, which would represent 1.6 g N deposition at the K:N ratio of fetal tissue (2.15:1). The average observed N retention was 2.4 g per day. The slope of the regression line relating N intake to retention indicated a low efficiency of N utilization, 30%; but predicted the same endogenous output, 1.73 g per day, in this group of pregnant adolescents as has been previously reported for nonpregnant college women.