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May 15, 2000 (Washington) -- It was one of the greatest inventions in fetal medicine, helping prevent an untold number of short- and long-term problems and deaths. But when electronic fetal monitoring during labor was introduced in 1968, it also had an unanticipated side effect -- an increase in the number of cesarean deliveries due to false alarms. And that's exactly where things have stood for over 30 years -- until Monday, when federal regulators approved a new type of fetal monitor that actually may take some of the guesswork out of deciding when a cesarean is necessary.
The optimism comes from the fact that the new monitor, OxiFirst Fetal Oxygen Saturation Monitoring System, directly measures the oxygen levels in the baby's blood. It consists of an infrared fetal sensor that is inserted into the mother's uterus and placed against the fetus's temple or cheek. In contrast, conventional monitors measure the fetal heart rate to give doctors an idea of the amount of oxygen in the baby's blood. On occasion, a fetal heart rate tracing can be difficult to interpret, and physicians may need to perform a cesarean section out of concern for the baby's well-being. They do not find out until after delivery that the babies, in most cases, had adequate oxygen levels.
"It is the first major technological development in fetal monitoring since electronic monitoring was introduced in the 1960s," Sharon Snider, an FDA spokesperson, tells WebMD.
In its primary clinical study of over 1,000 women, the device certainly did make a difference. The cesarean rate for non-reassuring heart rate, an indicator for when the baby may be having difficulty tolerating labor or may be in distress due to lack of oxygen, was twice as high in women monitored in the conventional way compared with those in the OxiFirst group.
According to the FDA's analysis, these results were seen because women monitored with the OxiFirst system were allowed to continue labor even when the fetus had a nonreassuring heart rate if the fetal oxygen level was above 30%. However, the study also found that the overall cesarean rate between the two groups was unchanged, and for reasons not explained in the study, that cesareans for dystocia (failure of the baby to pass through the pelvis) also increased in the OxiFirst group. One of the co-investigators, Gary Dildy, MD, said in an earlier interview that it is possible that some nonreassuring fetal heart rates may be an early indicator of the dystocia. Dildy is an associate professor of obstetrics and gynecology at the University of Utah Health Sciences Center in Salt Lake City.
At present, the OxiFirst system is indicated only for use along with conventional electronic monitoring, when the fetal heart rate is nonreassuring, Snider tells WebMD. It is also indicated for use only on single fetuses of at least 36 weeks gestation, after the bag of water has broken and the fetal head is in the normal vertex position, she says.
To further assess the effect of this monitor on cesarean rates, its maker has also been asked to conduct a large postmarketing study in general practice, she tells WebMD. All of these caveats were recommended by a group of FDA expert advisors, which reviewed the monitor in January.
Mallinckrodt Inc. of San Francisco makes the new monitor. The monitor will have a U.S. product launch Thursday, Barbara Abbett, a spokesperson for Mallinckrodt, tells WebMD.