Comparison of vaginal and transabdominal collection of amniotic fluid for fetal lung maturity tests.

Backgrounds: The lecithin/sphingomyelin (L/S) ratio and lamellar body count (LBC) are two tests that can be used to estimate the probability of the occurrence of respiratory distress syndrome (RDS). Our objective was to compare the prognostic capacity of the L/S ratio and the LBC in the prediction of RDS from amniotic fluid that was obtained either transabdominally or vaginally.

Methods: Consecutive women undergoing amniotic fluid sampling for determination of fetal lung maturity were included. In case the membranes were ruptured, amniotic fluid was obtained vaginally. Otherwise, amniotic fluid was obtained by transabdominal amniocentesis. In each specimen, an L/S ratio and a LBC were measured. The predictive capacity of specimens that were obtained vaginally and transabdominally were compared by calculating the area under the receiver-operating-characteristic curve (AUC) analysis.

Results: In 260 patients amniotic fluid was collected transabdominally, whereas in the other 67 patients there were ruptured membranes, and fluid was collected vaginally. RDS occurred in 25% of the patients without ruptured membranes, and in 34% of the patients with ruptured membranes. For the L/S ratio, the AUC was 0.56 (SE 0.09) for the vaginally collected specimens, and 0.93 (SE 0.02) in the specimens that were collected abdominally. For the LBC, the AUCs were 0.52 (SE 0.08) and 0.84 (SE 0.03), respectively.

Conclusions: Fetal lung maturity tests that are performed in vaginally obtained specimens in patients with ruptured membranes are of no use in the prediction of RDS.