Total protein concentration in human amniotic fluid is negatively associated with infant birth weight.

Our objectives were 2-fold: 1) to assess the concentration and distribution of total protein in human amniotic fluid (AF) using 3 standard assays [Bradford, bicinchoninic acid solution (BCA), and Lowry] and 2) to establish whether these total protein concentrations were associated with and predictive of infant birth weight. Birth outcomes were determined using recently developed birth-weight-for-gestational-age categories (percentiles) for fetal growth where infants < 10% were classified as SGA (small-for-gestational-age), those between 10 and 90% as appropriate-for-gestational-age (AGA) and those infants >/= 90% as large-for-gestational-age (LGA). AF samples were collected from women undergoing routine amniocentesis for genetic testing (mean = 15 +/- 0.04 wk, range 12-20 wk), frozen, and later analyzed for total protein in 617 singleton-expectant mothers in Montréal, QC, Canada. Maternal and fetal characteristics were obtained from questionnaires and medical chart review. Mothers giving birth to LGA infants had uniformly lower AF protein concentrations at 12-20 wk gestation compared with AF protein concentrations for mothers of AGA infants. Multiple regression analyses demonstrated that total AF protein, collected during routine amniocentesis and later analyzed by the Lowry method, was negatively associated with birth weight at term in our population. These data suggest that one or more AF proteins might emerge as biomarkers of fetal growth.