The effect on fetal arteriolar oxygen saturation resulting from giving oxygen to the mother measured by pulse oximetry


Dr N Johnson, Consultant Obstetrician, Leeds University, Leeds LS2 9NS, UK.


Objective To determine if pulse oximetry could detect any changes in fetal arteriolar oxygen saturation resulting from maternal administration of oxygen.

Design A prospective study comparing study comparing the fetal pulse oximetry reading before and after giving 27% and 100% oxygen to the mother. The data were collected using an experimental pulse oximeter and a sensor specifically adapted to cope with the problems of fetal pulse oximetry.

Setting Labour ward, St. James's University Hospital, Leeds University, UK.

Subjects Twelve fetuses presenting by the vertex in normal uncomplicated labour.

Main outcome measures The change in fetal arteriolar oxygen saturation recorded by the pulse oximeter in response to oxygen administration to the mother.

Results Twenty-seven percent oxygen increased the average fetal arteriolar oxygen saturation by 7.5%, the effect being reversed when the oxygen was withdrawn. One hundred percent oxygen increased fetal arteriolar oxygen saturation by 11% and when the oxygen was withdrawn oxygen saturation dropped by 10%. One hundred percent inspired maternal oxygen was more effective than 27%. The gradient of the fetal oxygen regression slope is steeper with 100% oxygen than 27% and it is steeper when oxygen is given compared to when it is withdrawn. This suggests that the fetus responds to the new placental oxygen gradient by accepting oxygen more rapidly than it gives it up. Using a quadratic regression model, it took 9 min for fetal oxygen saturation to reach its maximum value after giving the mother oxygen.

Conclusion This study confirms that a pulse oximeter is able to measure an increase in fetal arteriolar oxygen saturation when oxygen is administered to the mother.