Urinary excretion of some proteins and enzymes during normal pregnancy.

Total protein (TP), albumin (Alb), transferrin (TRF), retinol-binding protein (RPB), N-acetyl-beta-glucosaminidase (NAG), alanine aminopeptidase (AAP), gamma-glutamyltransferase (GGT), and creatinine (Cr) were measured in random (untimed) urine samples from 29 nonpregnant women and from pregnant subjects (11 in the first trimester, 34 in the second, and 37 in the third). The excretion of TP, Alb, TRF, NAG, and AAP (relative to creatinine) and the RBP concentration were all higher (P less than or equal to 0.05) in the second and third trimesters compared with values for the nonpregnant controls. The GGT/Cr ratio was significantly higher only in the third trimester. The increase in low-molecular-mass proteins and tubular enzymes suggests that at least part of the increase in Alb, TRF, and TP results from decreased tubular reabsorption. We conclude that excretion of both high- and low-molecular-mass proteins is increased during pregnancy.