THE OXYGEN STATUS OF FETAL BLOOD

Objective: To estimate the acid-base and oxygen status of fetal blood and compare with maternal placental venous blood. Data sources and cal culations: We selected pH and blood gas data from the literature perta ining to umbilical vein and artery blood obtained by cordocentesis and estimated values for the 30th and 40th gestational week. Average valu es for maternal venous blood Leaving the placenta were estimated on th e assumption of equal maternal arterio-venous and umbilical veno-arter ial total oxygen concentration differences. Results: pH and pCO(2) of maternal blood leaving the placenta and umbilical vein blood are almos t identical at week 30. A small pCO(2) and pH difference may exist at week 40. The pO(2) of the maternal placental venous blood and umbilica l vein blood are almost identical at week 30, but at week 40 a pO(2) d ifference indicates an umbilical arterio-venous shunting of as much as 30%. The fetal mixed venous pO(2) falls from 2.6 kPa to 2.2 kPa from the 30th to the 40th gestational week. Conclusion: More accurate measu rements are needed to confirm our results. Future measurements should be performed with a combined pH-blood gas analyser and haemoximeter to allow determination of the complete oxygen status of the blood.