The influence of maternal oxygen inhalation on human placental and umbilical venous blood flow.

The effect of maternal short-term inhalation of oxygen (51/min) on intervillous (IVBF) and umbilical vein blood flow (UVBF) was studied in 22 cases during the third trimester of pregnancy. The maternal paO2 levels increased significantly (P less than 0.001) after O2 inhalation. The mean IVBF level was 190 +/- 66 (SD) ml/min per 100 ml of the intervillous space before inhalation and 125 +/- 58 ml afterwards, the decrease being significant (P less than 0.01). UVBF maintained its original level after O2 inhalation. The human fetus seems not to compensate for alterations in oxygen delivery and reduced IVBF after maternal oxygen inhalation, by means of changes in UVBF.