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Engineers have built a wearable heart-rate monitor for unborn babies

Professional Engineering

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Engineers have built a wearable sensor that can monitor the heartbeat of an unborn child in the womb. It’s hoped it could reduce the estimated 2.6 million stillbirths per year worldwide.

A team at Stevens Institute of Technology in New Jersey used commercial sensors available in smartphones to orient the device, which can record vibrations sent through a mother’s abdomen when her baby’s heart beats, or when the foetus kicks, and which is potentially more accurate than currently available foetal heart-rate monitors.

“Almost a third of stillbirths occur in the absence of complicating factors," says Negar Tavassolian, an associate professor who led the work at Stevens. "Our device could let a pregnant woman know if her foetus is compromised and she needs to go to the doctor."

Many stillbirths are preceded by variations in foetal movement and heart-rate, and the researchers suggest that their device could be worn continuously during the final few weeks of pregnancy.

In a paper published in the IEEE Sensors Journal, the team report a study run in conjunction with two obstetricians from New York University’s Langone Medical Centre. In experiments on ten pregnant women, they found the device could detect foetal heart-rate with the same accuracy as foetal cardiotocograms, which are the current standard.

But while existing systems are bulky and expensive, and based on electrocardiogram and ultrasound technology, the team’s sensors are light and more efficient. One leading monitor system currently on the market weighs more than eleven pounds and has a battery life of four hours. The Stevens team’s device can run on a three-volt battery for more than a day.

The new monitor also poses no risk to the foetus -- a concern with ultrasound monitors, which can heat tissue if used continuously for long periods. The Stevens team's monitor simply detects existing vibrations, like a doctor listening with a stethoscope. "Our monitors are completely passive, so there's no health concern," Tavassolian says.

Previous work by Chenxi Yang, a graduate student at Stevens and first author on the paper, had shown that chest vibrations could be used to track an adult’s heartbeat, but it was thought that the movements of the mother’s own body would make it hard to use the same technology for unborn babies. The team combined signals from three different sensors and used algorithms to isolate the foetal heartbeat.

Vibration monitors can also offer an objective measure of foetal movement, which is currently assessed simply by asking mothers to count the times their baby kicks. Combining heart-rate and movement data could provide vital insights into foetal health, surpassing anything that's currently available, Yang explains. "That's the big plan -- to fuse these different modalities into a single device," he says.
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