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.