The Food and Drug Administration today approved a new type of fetal monitor that measures oxygen saturation in the baby's blood as a sign of fetal health during labor and delivery.

Conventional monitors used today measure fetal heart rate (FHR) and uterine contractions. Physicians use these measurements, along with other factors, to decide if labor can continue normally or if a Cesarean delivery is indicated.

The new monitor, the OxiFirst Fetal Oxygen Saturation Monitoring System, manufactured by Mallinckrodt/Nellcor Perinatal Business, Pleasanton, Calif., represents the first major technological development in fetal monitoring since electronic monitoring was introduced in the 1960's and '70s. The system builds on pulse oximetry technology initially developed in the 70's and 80's by Nellcor for adult and pediatric use.

The OxiFirst system is only to be used along with conventional electronic fetal monitoring when the fetal heart rate is "non-reassuring," i.e. when it indicates that the baby may be in distress due to lack of adequate oxygen. And it is intended for use only on single (not multiple) fetuses of at least 36 weeks gestation, where the mother's water has broken and the fetal head is in the normal vertex position for delivery.

The OxiFirst monitor consists of a fetal sensor that emits and detects red and infrared light, a connecting cable, and a microprocessor-controlled monitoring console. The monitor displays fetal oxygen saturation as the percentage of oxygen in the fetus's blood. During use, the OxiFirst sensor is inserted into the mother's uterus and placed against the fetus's temple or cheek.

FDA approval of the system was based on a review of a series of studies conducted by Mallinckrodt and on the recommendation of the Obstetrics and Gynecology Devices Panel of FDA's Medical Devices Advisory Committee, which met in January to review and evaluate this monitor.

In Mallinckrodt's primary study, 508 women were monitored with the OxiFirst monitor and 502 women received standard labor management without the OxiFirst monitor. Women monitored with the OxiFirst system were allowed to continue labor when the fetus had a non-reassuring heart rate and if the OxiFirst monitor showed that the fetal oxygen saturation was above 30 percent. The study assessed whether use of this new monitor would reduce the Cesarean-section rate due to non- reassuring fetal heart rate.

The primary objective of the study was met. It found that the Cesarean rate for non-reassuring heart rate was 10 percent in the group of women monitored conventionally compared to 5 percent in the OxiFirst group --a significant difference. However, the study also found that the overall Cesarean rate between the two groups was unchanged. For reasons not explained by the study, Cesareans for dystocia (difficult labor) increased in the OxiFirst group.

The study showed that the use of the OxiFirst monitor was safe for both the mother and fetus. The rate of adverse events was comparable between the two groups.

Some 3.8 million babies are born each year in the United States, and perhaps one-fourth of these represent women in labor with non-reassuring fetal heart rates, a key criteria for possible candidates for this new device.

To further assess the effect of use of this new monitor on Cesarean rates, Mallinckrodt will conduct a large study in general medical practice.