The correlation of ultrasonic placental grading and fetal pulmonary maturation in five hundred sixty-three pregnancies

In a previous study, it was suggested that the presence of a grade III placenta correlates 100% with a mature lecithin/sphingomyelin (L/S) ratio and may replace amniocentesis in confirming fetal lung maturity. In this study that hypothesis was tested in 563 pregnancies. All patients underwent amniocentesis and simultaneously had placental grading. The correlations of placental grade with an L/S ration ≥2 were: grade 0, 17%; grade I, 68%; grade II, 91%; grade III, 93%. The correlations of placental grade with the presence of phosphatidylglycerol (PG) were: grade 0, 17; grade I, 41%; grade II, 79%; grade II, 75%. The false positive rates associated with grade III placenta were, therefore, 7% for mature L/S ratio and 25% for PG present; when combined with a biparietal diameter ≥9.0 cm, a grade III placenta incorrectly predicted lung maturity in 8.5%. We conclude that placental grading is not accurate enough to replace amniocentesis as the standard test of fetal pulmonary maturity.