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Fetal O2 Monitoring Doesn't Change Outcomes or Cesarean Rates


DALLAS -- Fetal oxygen saturation monitoring doesn't alter the rate of caesarean deliveries or improve outcomes for newborns, researchers in a large randomized study reported.

DALLAS, Nov. 22 -- Fetal oxygen saturation monitoring doesn't alter the rate of caesarean deliveries or improve outcomes for newborns, researchers in a large randomized study reported.

When investigators monitored more than 5,300 women in first-time labor with fetal pulse oximetry, but randomly masked the data from half of the observers, there were no significant differences in outcomes or in Caesarean rates, reported Steven L. Bloom, M.D., of the University of Texas Southwestern Medical Center here, and colleagues elsewhere.

The delivery teams equipped with fetal oxygen saturation data and those kept in the dark acted similarly, the investigators reported in the Nov. 23 issue of the New England Journal of Medicine.

The findings suggest that fetal pulse oximetry may be another example of a technology that promises more than it delivers, they authors added.

"The widespread adoption of intrapartum electronic fetal monitoring in the early 1970s has been cited as an example of the incorporation of technology without proof of benefit," they wrote.

"The development of fetal oxygen saturation might improve understanding of fetal well-being during labor and thus reduce the rate of cesarean delivery for the indication of abnormal fetal heart rate," they continued. "Our trial confirms the value of rigorous assessment of new forms of technology by showing that knowledge of fetal oxygen saturation does not lead to a significant reduction in cesarean births overall or for the indication of a nonreassuring fetal heart rate."

In an accompanying editorial, Michael F. Greene, M.D, of the Massachusetts General Hospital in Boston agreed that those who seek a technological fix to the problem of fetal monitoring need to keep searching.

"The reduction in the rate of cesarean deliveries that were performed out of concern for intrapartum fetal asphyxia seen in previous studies was not observed in this trial, nor was there the enigmatic increase in cesarean deliveries for the indication of dystocia among women with non-reassuring fetal heart-rate patterns," Dr. Greene wrote.

"The performance of electronic fetal heart-rate monitoring as a screening test for fetal oxygen desaturation was poor. Neonatal outcomes were not significantly different between the groups."

Although electronic fetal monitoring is used in about 85% of all live births in the United States, its benefits, if any are uncertain, and critics maintain that it may contribute to the surge in caesarean deliveries, the authors noted.

Fetal pulse oximetry, approved conditionally by the FDA in 2000, was intended to provide continuous fetal oxygen saturation data when there is a "non-reassuring" fetal heart-rate pattern.

The device involves a sensor placed through the mother's dilated cervix after her membranes have ruptured. The sensor is placed against the fetus' face, and measures the fetus oxygen saturation levels during labor.

To determine whether knowledge of fetal oxygen saturation during labor would have an effect of clinical practice or fetal outcomes, the investigators conducted a multicenter study.

A total of 5,341 women who had never before given birth were enrolled at 14 centers. All women were assigned to electronic fetal monitoring with fetal pulse oximetry, but in half of the cases the investigators were blinded to the pulse oximetry data, while in the other half the clinicians were allowed full access to the data.

The investigators collected data on fetal heart-rate patterns before randomization, and used the information to stratify the study population into two groups: one with non-reassuring fetal heart-rate patterns, for whom fetal oximetry was primarily intended, and the other without fetal heart-rate abnormalities before the time of randomization.

They defined a non-reassuring fetal heart-rate pattern, using criteria from an earlier trial of fetal oximetry, as:

  • Severe variable decelerations (< 70 beats per minute for at least 60 seconds)
  • Late decelerations
  • Bradycardia (< 710 beats per minute)
  • Tachycardia (>160 beats per minute)
  • Diminished heart-rate variability (< 7 beats per minute over a period of at least 30 minutes)
  • One or more variable decelerations in two consecutive 30-minute windows
  • Increased heart-rate variability (>25 beats per minute over a period of 30 minutes)
  • Baseline rate of at least 100 to 120 beats per minute without accelerations
  • Suspected fetal arrhythmia.

An investigator at each site reviewed all fetal heart rate tracings.

They found that there was no significant difference in the overall rates of cesarean delivery between the groups, with 26.3% of women in the open group and 27.% in the masked group undergoing Caesarean section (P=0.31).

The rates of cesarean delivery associated with a non-reassuring fetal heart rate were also similar, occurring in 7.1% of cases in the open data group and 7.9% of cases in the blinded data group (P=0.30).

Rates of dystocia (i.e., abnormal or difficult delivery) too were similar, occurring in 18.6% of openly-monitored fetuses and 19.2% of fetuses monitored under cover (P=0.59).

When they considered the 2,160 women whose fetus had a non-reassuring heart rate before randomization, they found that the results were similar, with no significant differences between unmasked and masked labor.

There were no significant differences in maternal or infant complications or in the condition of the infants at birth.

"As with previous studies, application of the monitoring device was generally successful, was not associated with a high incidence of adverse effects, and was successful in obtaining the desired data about fetal oxygen saturation approximately 74% of the time the device was in place," the investigators wrote. "Unfortunately, knowledge of this additional fetal physiological information did not change the rates of cesarean or operative vaginal delivery in either the general study population of 5,341 women or the subgroup of 2,168 women with non-reassuring fetal heart-rate patterns."

In his editorial, Dr. Greene noted that the findings of no apparent benefit from an added technology provide an opportunity for regulators.

"Should the FDA's charge be minimalist and framed very narrowly, to approve a device that reliably does what it claims -- in this case, accurately record fetal oxygen saturation -- while not injuring people in the process?" he wrote. "Or should the FDA's charge be more expansive, to approve a new device only after it demonstrates some medical value added to the current standard of care?"

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