Blood gas analysis of placental and uterine blood during cesarean delivery

Objective: To measure blood gases in uterine venous blood and maternal and fetal blood from the placenta, and to characterize gas exchange in the intervillous space. Methods: Blood gas measurements were performed immediately after collecting placental and uterine blood from the subchorial and marginal lakes, from the chorionic vein and artery in the placenta in utero, and from the uterine vein during 12 cesarean deliveries. Results: The mean oxygen pressure (PO2) values of the chorionic vein and subchorial lake were 28.7 +/- 6.0 and 29.9 +/- 7.5 mmHg, respectively, with a difference of 1.2 mmHg. The individual data for PO2 of the chorionic vein exceeded those of the subchorial lake in five subjects and were almost equal in two of the 12 subjects. The mean values of carbon dioxide pressure (PCO2) and bicarbonate were greater in the chorionic vein than in the subchorial lake, but the mean pH values were the same in the two groups. The mean values of blood gas analysis were not different between subchorial and marginal lakes with similar blood composition. The mean PO2 of the uterine vein in ten subjects was 45.9 mmHg, significantly higher than that of the subchorial lake. Conclusions: The human placenta may be defined as a multivillous model with a high degree of oxygen transfer. Arteriovenous anastomoses are suspected in the pregnant uterus beyond 37 weeks' gestation. Subchorial and marginal lakes contain similar admired blood, which circulates and performs gas exchange.