|Technology for Monitoring Fetal Oxygen 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.)
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
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
“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.
The NICHD sponsors research on development, before and after
birth; maternal, child, and family health; reproductive biology
and population issues; and medical rehabilitation. For more information,
visit the Institute’s Web site at http://www.nichd.nih.gov/.
The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov.