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.