Fetal Oxygen Monitoring Technology During Labor Offers No Apparent Benefit
A new technology for measuring blood oxygen levels of a baby during labor - expected to provide information useful for preventing birth complications - offers no apparent benefit, report researchers in a National Institutes of Health research network.
The technology, known as fetal oxygen saturation monitoring, was designed for use along with electronic fetal monitoring, which tracks the fetal heart rate, to measure changes in fetal oxygen levels. Designers of the new technology hoped that knowing the oxygen status of the baby during labor would provide information on the health of the baby, especially when there were disturbances in the fetal heart rate during labor.
"The results of this study show that while a new technology may appear to be very promising, it's not possible to know how effective it will be until it can be fully tested under clinical conditions," said Duane Alexander, M.D., Director of NIH's National Institute of Child Health and Human Development, which operates the network.
The study, appearing in the November 23 New England Journal of Medicine, was conducted by researchers in the NICHD Maternal-Fetal Medicine Units Network. The study's first author was Steven L. Bloom, M.D., of the University of Texas Southwestern Medical Center in Dallas.
"Fetal oxygen saturation monitoring offered no apparent advantage in interpreting the meaning of abnormal fetal heart rates," said Catherine Spong, M.D., an author of the study and Chief of NICHD's Pregnancy and Perinatology Branch. "Abnormal oxygen readings were common among babies showing abnormal heart rates but they were also common among babies with normal heart rates."
The study authors noted that a technology developed earlier, electronic fetal heart rate monitoring, was adopted for use in delivery rooms without prior testing. Although electronic fetal heart rate monitoring is in widespread use, the study authors added, there is controversy about the technique's effectiveness.
The authors of the current study undertook their research to try to find if there was sufficient reason to warrant introducing fetal oxygen saturation monitoring into the delivery room. A previous study of the technology was inconclusive. That study found no overall change in Caesarean delivery rates when fetal oxygen saturation monitoring was undertaken. However, the study found different rates of Caesarean deliveries for two different categories of births. For cases in which the fetal heart rate pattern was abnormal, there were fewer Caesarean deliveries than normal. But there was a higher-than-normal rate of Caesarean deliveries from cases involving dystocia--failure of the baby to move down the birth canal. (Dystocia can result from such causes as the baby being improperly positioned in the birth canal, or from the baby simply being too large.)
Because the results of that earlier study were inconclusive, the U.S. Food and Drug Administration, which approves new medical devices for safety and effectiveness, granted only provisional approval for fetal oxygen saturation monitoring until the new technology could be proven effective. The current study was designed to settle unresolved questions about the new technology.
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.