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ObjectiveThe purpose of the study was to examine whether the acid-base balance in amniotic fluid reflects the acid-base state in fetal blood.Study designThe pH, PCO2, PO2, bicarbonate, and base excess concentrations were measured in umbilical venous, umbilical arterial, and maternal venous blood and in amniotic fluid samples obtained at fetoscopy. This was performed before intraamniotic termination of 16 normal pregnancies (mean gestation 19.4 weeks), as well as in 14 red blood cell isoimmunized pregnancies (mean gestation 28.4 weeks) undergoing fetoscopy for the diagnosis and treatment of fetal anemia.ResultsIn normal pregnancies, amniotic fluid pH and bicarbonate were significantly lower than umbilical venous and umbilical arterial blood concentrations, and this was due to the high concentration of base deficit in amniotic fluid. Whereas amniotic fluid PCO2 did correlate significantly with fetal umbilical venous PCO2 values, there was no correlation between other acid-base characteristics.ConclusionSimultaneous sampling of human fetal umbilical blood and amniotic fluid under the acute conditions of this study did not show significant correlations in acid-base values.

Original publication




Journal article


American journal of obstetrics and gynecology

Publication Date





970 - 973


Nuffield Department of Obstetrics and Gynaecology, John Radcliffe Hospital, Headington, Oxford, England.


Amniotic Fluid, Fetal Blood, Humans, Carbon Dioxide, Acid-Base Equilibrium, Pregnancy, Hydrogen-Ion Concentration, Partial Pressure, Female