Diagnostics & Imaging Week Washington Editor

Post-market studies are a typical condition of device approvals by the FDA, and most sponsors certainly enter those post-market studies with some degree of confidence that their product will stand up to clinical scrutiny.

But it does not always work out that way.

One recent post-market trial offered results that were anything but what doctors, expectant mothers and the sponsor wanted. The outcome of the trial suggested that oxygen value data via a fetal monitor are of little help in determining a baby's health just prior to birth, and as a result Nellcor (Pleasanton, California) has taken a minor hit.

Kristin Garvin, the director of marketing communications at Tyco Healthcare (Mansfield, Massachusetts), told Diagnostics & Imaging Week that while "the OxiFirst system has been a valuable assessment tool for the limited number of clinicians who utilize the system," the firm is nonetheless "not actively pursuing a fetal monitoring product" and is no longer selling the OxiFirst. She said she could not disclose the number of units currently in the market.

The Nov. 23 edition of the New England Journal of Medicine featured an article on the follow-up trial for the OxiFirst, a fetal oxygen saturation monitor made by Nellcor, which earned an FDA approval in March 2000 when the company was part of Mallinckrodt (Hazelwood, Missouri) and before Mallinckrodt was absorbed by Tyco.

The OxiFirst was implanted in all the mothers who enrolled in the trial, but the data were displayed to the doctors of only half the enrollees. Despite the difference in data availability, "there was no significant difference in the overall rates of caesarean delivery between the open and masked groups," according to the report of the trial. Those women whose attending clinicians saw the oximetry data had C-sections 26.3% of the time, compared to 27.5% of the patients whose doctors were blinded.

When data were broken down for mothers whose babies exhibited irregular heartbeats or who otherwise showed signs of a distressing delivery, the presence of information on oxygen saturation fared no better. And analysis of a trial subgroup also offered no reassurance for fetal oximetry.

Steven Bloom, MD, and colleagues wrote that even among women who were randomized after tests indicated "non-reassuring" heartbeats in the fetus, "the condition of the infants at birth did not differ significantly" between those in this group who were monitored and those who were not.

Bloom is an associate professor of obstetrics and gynecology at the University of Texas Southwestern Medical Center (Dallas).

Another scientist who participated in the study, Catherine Spong, MD, chief of the pregnancy and perinatology branch at the National Institute of Child Health and Human Development, highlighted the underlying dilemma for clinicians presented by oximetry study data in remarking that while "abnormal oxygen rates were common among babies showing abnormal heart rates . . . they were also common among babies with normal heart rates."

Fetal oxygen levels came to the fore over the past couple of decades as a potential harbinger of a variety of health problems, and fetal heart monitoring was promoted as a more or less reliable way to gauge oxygen saturation in the fetus.

Unfortunately though, this assessment strategy picked up a reputation for false negatives, which some observers came to believe played a role in the seemingly endless increase in C-section births.

According to the National Center for Health Statistics at the Centers for Disease Control and Prevention (Atlanta), more than 30% of all births were via C-section in 2005, up from 29.0% the previous year and from 22.7% in 1990.

The hope was that when paired with fetal heart monitors, fetal oximeters could tell clinicians when a baby was at risk despite seemingly normal hearth rhythm and should be delivered via C-section, but also could also weed out some of the false positives rendered by fetal heart monitors.

However, a preliminary trial for the OxiFirst was inconclusive as to whether oxygen saturation was of clinical significance, and the just-published study seems to answer that question decisively in the negative. With no discernible difference in the rates of C-section births between the two groups, fetal oximetry seems to have nowhere to go.

Duane Alexander, MD, the director of the National Institute of Child Health and Human Development, said the outcome of the study "shows 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."

Despite the non-significant outcome, Bloom was not ready to write off fetal oximetry altogether. While the investigators "found absolutely no difference in Caesarean sections" and depicted "no apparent benefit of this technology," he noted that the outcome does not suggest that "there won't be possibilities in the future."

On the other hand, at least one observer is of the opinion that cardio-pulmonary metrics have little to do with the rise in C-sections.

Michael Divon, MD, the chair of obstetrics and gynecology at Lenox Hill Hospital (New York), pointed out that fetal oximeters are not commonly used in the U.S. and described the trial as "somewhat irrelevant because so many C-sections are elective." And he saw little probability that C-sections will fall because "so many are being done just because the patient wants it."

Nellcor's Spong sees the question of C-section prevalence somewhat differently. She told D&IW that the question of whether C-sections are primarily elective procedures is "a very valid question" for further investigation. But she was nonetheless of the opinion that "purely elective C-sections are a very small portion" of the total number of C-sections in the U.S.

In 2005, the American College of Obstetricians and Gynecologists (Washington) chimed in on the fetal heart rate monitoring question, pointing out that "the false-positive rate . . . is high" and that "electronic fetal monitoring increased the likelihood of cesarean delivery and the use of vacuum or forceps" compared with the use of a stethoscope to track fetal heartbeat. Nonetheless, ACOG was cool to oximetry even then, stating that "because of concerns about false reassurance of fetal oxygenation, use of fetal pulse oximetry is not recommended at this time."

The news does not seem to have made investors particularly happy. The firm's shares closed at $3.15 on Nov. 22 and dropped further to $3.01 at market close yesterday. However, according to Quote.com, the analyst's consensus is that the firm is rated a buy, with anticipated long-term growth rate of 13%.

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