The same heightened electrical activity that indicates an adult taking a treadmill test isn’t getting enough oxygen to his heart is now being measured during labor to see if it can better identify babies in serious distress who need immediate delivery.
The Medical College of Georgia in Augusta is the lead site in the nation to help determine whether monitoring ST segment activity during labor reduces the number of babies born with hypoxic brain damage as well as unnecessary Caesarean sections.
“The umbilical cord, the brain and the heart are the particular aspects of the fetus that have to be conserved almost at all costs to maintain life,” says Dr. Lawrence D. Devoe, Brooks Professor and chair of the MCG Department of Obstetrics and Gynecology. “When you start seeing changes in the heart that suggest an oxygen deficit, such as elevations in the ST segment, that means your ability to handle an overall lack of oxygen has been exceeded and your defenses are beginning to crumble.”
Dr. Devoe is a principal investigator on the study of a device that combines this ST segment monitoring – which also is measured in an electrocardiogram, or ECG, – with the standard fetal heart rate monitoring performed on 80 to 90 percent of the 3.2 million babies exposed to labor in the United States each year.
Typical heart rate monitoring includes putting an ultrasound unit on the mother’s abdomen or an electrode on the baby’s head via the vagina to pick up fetal heartbeat, which is translated into a pattern. Although obstetricians know certain heart rate patterns indicate stress, “it’s a pretty big leap from seeing these patterns to knowing for sure that oxygen delivery to the baby’s brain is being interfered with,” Dr. Devoe says. In fact, about half the time doctors see the abnormal heart rate, the baby is in no immediate danger.
Heart rate monitoring alone also can provide a horribly false sense of security. “A baby that is stressed early on would raise his heart rate,” Dr. Devoe says. “But as the stress period becomes more intense, the baby’s ability to sustain that heart rate goes down. It’s like a runner. Initially, your heart rate goes up because you are trying to deliver more oxygen, but you may reach a point where you hit a wall and you can’t do it anymore.”
The STAN® S21 Fetal Heart Monitor system, designed by Sweden-based Neoventa, Inc., now under study in some 800 labors in the United States, seems to take some of the educated guesswork out of whether there is a real problem and helps physicians make better decisions quicker, Dr. Devoe says.
Previous studies during about 8,000 labors in England and Sweden found a 50 percent reduction in babies born with abnormal blood gasses, a 20 percent reduction in unnecessary C-sections and no hypoxic brain damage in babies monitored during labor with the device.