A new study has indicated that fetal oxygen monitoring does not improve outcomes during childbirth. The randomized, controlled study was large, involving 14 hospitals and over 5,000 subjects, and the results have been published in an article and editorial in the New England Journal of Medicine. The study had been designed to enroll 10,000 subjects, but the findings were so clear that it was halted early.
The hope behind the technology was that by monitoring both heartrate and oxygen level, obstetricians would be able to discern which babies were truly in an emergency situation, thus lowering the rate of Cesarean sections. That is, the additional monitor, it was hoped, would correct for the failure of heartrate monitoring alone to lower infant mortality rates and the rate of complications such as cerebral palsy. The fetal oxygen monitor will now be discontinued.
This study is important because it was performed before the technology was widely adopted, in contrast to fetal heart monitoring. A number of studies have shown that routine fetal heart monitoring, too, is no better at predicting fetal distress than a trained nurse with a fetoscope, but that it does increase a woman's chance of having a C-section (not to mention that it constrains a woman's movement during labor and that internal monitoring is an invasive procedure for both mother and fetus). Nonetheless, obstetricians have come to rely on fetal heart monitoring, and 85% of births are so monitored. The C-section rate rose again last year to 30.2% of all births, a 46% rate increase in a decade. (An editorial about the shortcomings of fetal heart monitoring, with references, is here.)