Subamnionic vernix caseosa.
Vernix caseosa occasionally dissects underneath the amnion, presumably following rupture of the amnion prior to rupture of the chorion laeve. We describe the clinicopathological features of 18 cases in which large quantities of vernix caseosa were present beneath the amnion of the parietal membranes or the chorionic plate. The subamnionic vernix caseosa was an unexpected microscopic finding in each case and was not associated with any inflammation, giant cell reaction, or other chronic change in the adjacent membranes. The gestational age ranged from 29 to 42 weeks (mean, 37). Five (28%) of the 18 were twin pregnancies. Five (28%) were delivered by cesarean section. In no case was there a history of amniocentesis, prolonged rupture of membranes, or amnionic fluid leakage. None of the mothers had signs of amnionic fluid embolism. The absence of tissue response around the vernix caseosa suggests rupture of the amnion close to the time of delivery.