Listening to a Fetus’s Heartbeat

Discerning the heartbeat of a baby still in the womb is a bit like making out a murmur in a crowded room. However, researchers at the University of Nottingham have designed a fetal heart monitor that can accurately distinguish a fetus’s heart rate from its mother’s and from surrounding noises. What’s more, they’ve made the device noninvasive, small, and easy to use in the home. Scientists have also enabled the monitor to transmit heart-rate data to the Internet, where doctors can remotely analyze and watch particularly high-risk pregnancies.

Since the 1950s, Doppler ultrasound has been the main method for monitoring fetal activity. By applying ultrasonic waves to the mother’s abdomen, clinicians can measure a fetus’s blood flow and heart rate. However, the technique has its downside. It takes an expert to operate and interpret data from ultrasound machines, and the procedure can only be performed in a hospital setting. Some experts also say that the technology does not accurately pick out a fetus’s heartbeat.

“Doppler heart-rate assessment relies on an average of mechanical heart movements detected by ultrasound,” says James Smith, clinical associate professor of obstetrics and gynecology at Stanford University. “Thus, an assessment of true ‘beat-to-beat’ variability, an indication of adequate oxygenation within the fetus, is limited.”

So scientists at the University of Nottingham, led by associate professor Barrie Hayes-Gill, have designed a highly sensitive fetal monitor that measures the electrical activity of a fetus’s heart, at the scale of nanovolts. Hayes-Gill and his colleagues have created a spinoff company, called Monica Healthcare, to explore the device’s commercial applications.

Terence Martin, the company’s chief marketing officer, says that the device, which is about the size of an iPod, is fairly simple in concept. “Essentially, the electrical signals from the beating fetal heart make their way to the mother’s abdominal surface, so you can pick up fetal signals from placing electrodes on the mother’s stomach,” says Martin.

However, scientists found that getting a clear signal wasn’t merely a matter of listening in on one electrode. The average fetal heartbeat can be detected at around 0.2 microvolts, whereas the mother’s heartbeat is around 100 microvolts. Normal muscle contractions also contribute to the surrounding “noise,” as does any electrical interference from the monitoring device itself.

Martin adds that a fetus’s gestational age can also be an obstacle to getting accurate readings. “The difficult period is between 28 and 30 weeks because there’s evidence that the fetus gets covered in this waxy substance and is totally insulated, so the signals get absolutely minute in that period.”

To clear these hurdles, Nottingham researchers worked to design a low-noise apparatus, consisting of a digital-processing body, leads, and electrodes. They then found that using more than two electrodes increased their chances of detecting a fetal, as well as a maternal, heartbeat. The fetus’s heart rate emerged after scientists applied a heart-rate extraction algorithm to the data, in effect subtracting the mother’s large heartbeat from the overall output. They could then identify the smaller peaks and amplitudes, indicating the fetus’s heartbeat.

Hayes-Gill and his colleagues tested an initial device on 400 pregnant women. They are currently testing the most recent prototype, which they hope to launch commercially, on 44 women, all within 28 to 32 weeks of pregnancy. During the experiments, the women are asked to wear the monitors, with electrodes taped to their abdomens, for 16 to 20 hours. During the day, the women are instructed to go about their normal activities, barring bathing and showering. The device itself has no display but is Bluetooth enabled to send data to a PC, where scientists can analyze the data with heart-rate extraction software. Martin says that so far, scientists have been able to accurately identify fetal heartbeats 90 percent of the time.

“A mother can walk around, sleep, do what she wants,” he says. “We can monitor mothers at home very easily because the device doesn’t require supervision, and there’s no skill required to stick the electrodes on.”

Eventually, Martin envisions selling the user-friendly, handheld monitor to hospitals and private practices, where doctors can prescribe them to high-risk mothers and analyze the incoming data for any irregularities. He anticipates that the device will be on the market in Britain by September and in the United States by the summer of 2008.

“This technology could be a much-needed improvement to existing methods of fetal monitoring,” says Tammy Euliano, associate professor of anesthesiology, obstetrics, and gynecology at the University of Florida at Gainesville. “However, reliability will be vital in that inaccurate recordings could lead to a false sense of security regarding fetal well-being, or, more likely, [to] undue concern, repeated calls to the OB, and/or trips to the hospital.”