Correlation of real-time ultrasonic placental grading with amniotic fluid lecithin/sphingomyelin ratio.

Placental grading with real-time ultrasound was performed on 235 patients who underwent amniocentesis for determination of the lecithin/sphingomyelin (L/S) ratio between 31 and 44 weeks' gestation. Grades I, II, and III placentas were encountered in 88, 72, and 75 patients, respectively. Forty-eight percent of Grade I, 69% of Grade II, and 92% of Grade III placentas had mature L/S ratios (L/S greater than or equal to 2.0). All of the 52 patients with a Grade III placenta who underwent repeat cesarean section at term gestation had mature L/S ratios. However, 37% of the pregnancies complicated by maternal or fetal disease, with Grade III placentas, had immature L/S ratios. The gestational age of these six patients ranged from 34 to 37 weeks. These results suggest that a Grade III placenta in normal term gestation has a good correlation with fetal pulmonary maturity as predicted by the amniotic fluid L/S ratio.