December 4, 2006

No Apparent Benefit to Monitoring Fetal Oxygen During Labor

Picture of pregnant woman and child

Electronic fetal monitoring is widely used to track the fetus's heart rate during labor. More recently, a technology called fetal oxygen saturation monitoring was developed to measure the level of oxygen in the baby's blood. Doctors hoped that adding oxygen monitoring during labor would provide them with more information on the baby's health to prevent birth complications. A new study, however, shows that the new technology offers no apparent benefit.

In 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. The U.S. Food and Drug Administration granted approval of the OxiFirst Fetal Oxygen Saturation Monitoring System on May 12, 2000. However, a previous study of the technology was inconclusive about the technique's effectiveness.

To further explore fetal oxygen saturation monitoring, researchers in the Maternal-Fetal Medicine Units Network, which is operated by NIH's National Institute of Child Health and Human Development (NICHD), enrolled 5,341 women from 14 hospitals throughout the U.S. 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

The researchers reported in the November 23 issue of New England Journal of Medicine that there were no significant differences in Caesarean delivery rates or the condition of the infants at birth between the groups. In the open group, 26.3% 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 situations in which the baby fails to move down the birth canal. Fetal oxygen saturation monitoring produced no significant difference in these subgroups, either.

The procedure itself caused some complications. 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.

“Fetal oxygen saturation monitoring offered no apparent advantage in interpreting the meaning of abnormal fetal heart rates,” said Dr. Catherine Spong, 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.”

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