The U.S. Food and Drug Administration granted approval of the OxiFirst Fetal Oxygen Saturation Monitoring System on May 12, 2000. As a condition of the approval, FDA required that the manufacturer of the device conduct additional studies to resolve questions on the device’s effectiveness and its potential influence on the rate of Caesarean deliveries.

With fetal oxygen saturation monitoring, a sensor is inserted by hand through the cervix, after the membranes have ruptured, and placed against the baby’s face. The sensor, connected to a monitor by a cable, provides a continuous reading of the baby’s oxygen level.


For the current study, the researchers enrolled 5341women from 14 hospitals throughout the United States. The women were randomly assigned to one of two groups: an “open” group, in which oxygen levels were continuously monitored, and a “masked” group, in which oxygen levels did not appear on a monitor and were not revealed to birth attendants. Of the pregnant women who participated, 2629 were randomly assigned to the open group and 2712 women were assigned at random to the masked group.

Overall, the researchers found no statistically meaningful differences in Caesarean delivery rates between the groups. In the open group, 26.3 percent of deliveries were by Caesarean, versus 27.5 in the masked group. The researchers also compared Caesarean rates for two subgroups in the study, babies experiencing a disturbance in fetal heart rate and women experiencing dystocia. Again, the use of fetal oxygen saturation monitoring produced no statistically meaningful difference in Caesarean delivery for infants with a disturbance in fetal heart rate, (7.1 percent for the open group, 7.9 percent in the masked group). Differences in Caesarean delivery rates for dystocia also were not statistically meaningful between the two groups (18.6 percent for the open group, 19.2 percent, for the masked group).

In 170 cases, the researchers were unable to position the sensor against the baby’s face. In 40 cases, insertion of the sensor caused the baby’s heart rate to slow down, potentially jeopardizing the ability to provide sufficient blood and oxygen to the tissues. The researchers theorized that such drops in heart rate might have been caused by inadvertent pressure on the umbilical cord when inserting the sensor, or because of manipulation of the baby’s head.

“In this study of more than 5000 women delivering at 14 university hospitals throughout the United States, knowledge of intrapartum fetal oxygen saturation had no significant effect on the rates of Caesarean delivery overall or specifically for the indications of a nonreassuring fetal heart rate or dystocia,” the authors wrote.

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