Pulmonary maturity studies in the evaluation of premature labor

Amniocentesis was performed in 25 patients being treated with tocolytic therapy for premature labor, in an effort to determine the incidence of patients with mature lecithin/sphingomyelin (L/S) ratios and to discover a possible effect of tocolytic therapy on pulmonary maturity studies. Optical density measurements at 650 nm (OD650) and L/S ratio determinations were performed on the amniotic fluid. Repeat amniocentesis was performed in eight patients from 48 hours to 7 days after initiation of tocolytic therapy. There was a poor correlation between OD650 values of 0.150 or greater and L/S ratios of 2 : 1 or greater (64.3% false positives); and in the eight patients who underwent repeat amniocentesis, there was no significant change in the L/S ratio.