Study Finds No Value in Fetal Oxygen Monitors

A large new study indicates the fetal oxygen monitor is essentially worthless. It was hoped the monitors would lead to healthier infants or fewer C-sections for expectant mothers.

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Doctors have long tried to figure out how to tell when a fetus is in danger during childbirth. Thirty years ago, they thought they had the answer - a gadget called an electronic fetal monitor. But those monitors don't catch many problems and sometimes, they prompt obstetricians to perform unnecessary Caesarians.

Now, as NPR's Richard Knox Reports, a newer type of fetal monitor hasn't turned out the way many expected either.

RICHARD KNOX: This is a tale about how new medical technologies get accepted and sometimes, how they don't. In this case, the technology is used in one of medicine's most high stakes events -

(Soundbite of baby crying)

KNOX: - the birth of a baby. In the 1960s, doctors figured out a way to eavesdrop on the fetus's heart.

(Soundbite of fetal heart monitor)

Dr. MICHAEL GREEN (Massachusetts General Hospital): What you're hearing is the sound of the fetus's heart beating.

KNOX: Dr. Michael Green is standing at the bedside of a woman in labor at the Massachusetts General Hospital. Encircling her belly is the belt of an electronic fetal monitor. It uses ultrasound to track fetal heart rate, unfurling a beat-to-beat record. Almost every woman who gives birth in a hospital wears one of these monitor belts.

Dr. GREEN: In this situation, with a normal fetal heart rate pattern, we would consider that very reassuring of fetal well being.

KNOX: Has it resulted in better outcomes?

Dr. GREEN: No - that's the problem.

KNOX: Fetal heart monitors have been a disappointment. But even so, any doctor could be in big trouble if he had to admit in court that he hadn't monitored a delivery that went bad, so nobody is talking about junking fetal heart monitors.

It's a different story with a newer type of monitor. In the late 1990s, researchers developed what they thought was a better way to tell if a fetus is in distress. It uses a sensor taped to the fetus's head to measure the amount of oxygen in the fetus' blood.

Dr. GREEN: The great hope was that direct fetal oxygen monitor could give us the information we thought we really wanted to know - the amount of oxygen in the fetus's blood at any time, rather than sort of an indirect measure, namely, the fetal heart rate.

Dr. STEVEN BLOOM (University of Texas Southwestern Medical Center): This made a lot of intuitive, as well as physiological sense -

KNOX: Dr. Steven Bloom is Chief of Obstetrics at the University of Texas Southwestern Medical Center in Dallas. Six years ago when the FDA approved the new fetal oxygen monitor, it urged further study to find out what impact it would have in the real world. The FDA wanted to know does the device avoid unnecessary Caesarians by reassuring doctors that an odd sounding heart rhythm is not really a problem, and does it prevent devastating disorders, such as cerebral palsy, by signaling that a fetus truly is in trouble.

Steven Bloom led a study to find out. It enrolled more than 5,300 women around the country. All of them had fetal oxygen monitors during labor, but half of the time, the machine's readout was concealed from the obstetricians. The outcome is in this week's New England Journal of Medicine.

Dr. BLOOM: We found no evidence that knowledge of baby's oxygen level, that is, how much oxygen was in the baby's bloodstream, impacted the rate of Caesarian delivery, and we found that information about the baby's oxygen level made no difference in the baby's outcome.

KNOX: The oxygen monitor is worthless. The study provides an important clue as to why a third of fetuses did have low oxygen levels during labor but that was no problem for the vast majority of them. Fetuses are very resilient, that's why it's so hard to sort out the real alarms from the false. Michael Green at Massachusetts General says the new study is definitive.

Dr. GREEN: I think that the story is over as far as routinely measuring fetal oxygen level on normal, healthy laboring patients.

KNOX: The interesting, though, is that unlike fetal heart monitoring, this time, the new technology didn't take off before the evidence of its value was in. Only a few hundred U.S. hospitals are thought to have bought the oxygen monitors. As a result, the company that makes them quietly took them off the market earlier this year. Sometimes, Green says, doctors do learn from their mistakes.

Richard Knox, NPR News, Boston.

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