Amniotic fluid particles: are they related to a mature amniotic fluid phospholipid profile?

In a prospective, blinded clinical study, the relationship between amniotic fluid free-floating particles measured by a dynamic ultrasound imaging method and phospholipid profile was studied in 82 women undergoing amniocentesis between 26-42 weeks' gestation. None of 11 patients with sonographically clear amniotic fluid had a mature phospholipid profile (lecithin-sphingomyelin ratio greater than 2 and detectable phosphatidylglycerol). Thirty-eight of 71 women (53%) with turbid or markedly turbid amniotic fluid had a mature phospholipid profile. The sensitivity of this method was 100%, specificity 25%, positive predictive value 53%, and negative predictive value 100%. Although the finding of sonographically clear amniotic fluid may eliminate unnecessary amniocentesis, markedly turbid amniotic fluid is not a reliable indicator of a mature amniotic fluid phospholipid profile.