Assay of disaturated phosphatidylcholine in amniotic fluid as a test of fetal lung maturity: Experience with 2000 analyses

We determined concentrations of disaturated phosphatidylcholine (DSPC) in nearly 2000 amniotic fluid samples obtained either transabdominally or as vaginal pools. Here we report our comparison of these DSPC values with the lecithin/sphingomyelin (L/S) ratios for amniotic fluid samples obtained from diabetic and nondiabetic pregnancies and also between transabdominally or vaginally collected samples uncontaminated by blood or meconium. DSPC measurement is at least as good as the L/S ratio in predicting the absence of respiratory distress syndrome. DSPC concentrations were, however, lower in diabetic than in nondiabetic pregnancies, supporting the hypothesis that DSPC synthesis may be impaired in fetuses of diabetic mothers. Visually uncontaminated samples collected transabdominally or vaginally, when grouped according to length of gestation, have similar DSPC values but different L/S ratios. Thus, even in the absence of blood or meconium, DSPC may be a more useful test than the L/S ratio for vaginally pooled samples.