Amniotic fluid Clara cell protein concentration in normal pregnancy, a marker of fetal airway growth or fetal lung maturation?

Abstract

To evaluate the relationship of Clara cell protein (CCP) in amniotic fluid (AF) with the lecithin/sphingomyelin (L/S) ratio, and the concentrations of saturated phosphatidylcholine (Sat PC) and surfactant protein A (SP-A). AF samples were obtained by amniocentesis from 98 pregnancies without conditions known to influence fetal lung maturation between 25 and 41 weeks of gestation. These samples were used for determinations of CCP, L/S ratio, Sat PC, and SP-A. Simple and multiple linear regressions were used to analyze the data. CCP in AF increased logarithmically with gestational age (R(2)=0.51, p=0.006). The L/S ratio (R(2)=0.41, p<0.001), and the concentrations of Sat PC (R(2)=0.26, p<0.001) and SP-A (R(2)=0.52, p<0.001) also increased with advancing gestation. Weak correlations of CCP with the L/S ratio (R(2)=0.22, p=0.009) and Sat PC (R(2)=0.12, p=0.004), but not with SP-A (R(2)=0.07, p=0.10), were found. Using multiple linear regressions, gestational age was the only predictor of CCP (F=10.9, R(2)=0.13, p=0.015). Conversely, gestational age, Sat PC, and SP-A accounted for most of the variation of the L/S ratio (F=34.7, R(2)=0.61, p=0.0001). CCP correlated very poorly with known and widely accepted indices of fetal lung maturation. The increasing concentration of CCP in AF throughout gestation probably reflects growth and development of the fetal airways.