The sonolucent placenta in high-risk obstetrics.

Placental sonolucency has been reported to be a normal sonographic finding after 36 weeks' gestation. To further characterize this acoustic phenomenon, 15 placentas from previously scanned high-risk obstetric patients were studied in vitro. Placentas were obtained at delivery, and were washed, weighed, sonographically imaged in a water bath, x-rayed by xerography, and pathologically examined. Placental sonolucency occurred as early as 31 weeks' gestation and corresponded anatomically to cotyledons. The degree of septal calcification appeared to correlate best with the degree of sonolucency, and no unusual gross or microscopic placental features could be identified. Intrauterine growth retardation or intrauterine fetal death occurred in 8 of the 10 patients in whom there were sonolucent changes.