Placental water content and distribution.

The percentage of total placental water (%H2O(T)), maternal (%MBV) and fetal (%FBV) blood volumes, non-vascular extracellular (%EW) and intracellular (%IW) water, and villous histology were studied in placentas from 12 normal term pregnancies after a normal vaginal delivery, 19 caesarean sections at term after a normal pregnancy and history of a previous caesarean section and 47 caesarean sections at term or preterm due to pregnancy complications. Values were derived from change in placental dry weight, maternal and fetal haemoglobin content and 51CrEDTA space after incubation of placental fragments. Normal ranges (mean +/- SD) after term vaginal delivery were: H2O(T) 83.9 +/- 0.2%, MBV 10.9 +/- 0.2%, FBV 7.4 +/- 0.9%, EW 57.3 +/- 1.3% and IW 11.2 +/- 0.6%. %H2O(T) was higher after caesarean section; other measurements were not affected. There were no differences between placentas after 33-37 and after 38-42 weeks gestation. Three of eight placentas after rhesus incompatibility had %H2O(T) above the mean +2SD of term placentas and five of 17 IUGR placentas were below the mean -2SD. The remaining placentas following maternal pre-eclampsia, hypertension, or diabetes had no apparent alteration in %H2O(T). A blind histological diagnosis of 'true' oedema was associated with both a significantly high %IW and %H2O(T). Perhaps this is due to alteration in placental cell volume regulation in certain situations.