Listening to a Fetus's Heartbeat

A device the size of an iPod could give women with high-risk pregnancies a way to monitor the health of the fetus.

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.

Baby heartbeats: An iPod-size fetal heart monitor developed by researchers at the University of Nottingham can pick up the minute heartbeats of a fetus, wirelessly transmitting the data to physicians via the Internet. Credit: Martin Kirk, University Nottingham

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.

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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."