A wearable patch could let doctors monitor a foetus remotely, hope researchers at Stanford Medicine, the University of California San Diego and Oxford University.

They have developed the wearable ultrasound patch to monitor pregnancies. The patch adheres to a patient’s abdomen to provide continuous, real-time information about blood flow in the foetus and umbilical cord.

The patch is a flexible adhesive sticker, about the size of the palm of a hand, that adheres to the abdomen. It is connected by a cable to a computer that interprets ultrasound data. The researchers think the patch will initially be used for pregnant women who are hospitalised, but they hope eventually to have a wireless version that enables doctors to monitor patients at home.

The device, whose design and early validation in several dozen pregnant patients was published in Nature Biotechnology, holds promise for helping doctors monitor conditions such as intrauterine growth restriction, which affects 10% of all pregnancies. In this pregnancy complication, the foetus grows slowly due to limited oxygen or nutrients, a result of insufficient blood flow through the umbilical cord. In severe cases, doctors deliver the baby early to enable better growth or avert stillbirth.

“There’s nothing similar to our device on the market or in the scientific literature,” said senior study author Sheng Xu, professor of anaesthesiology at Stanford Medicine. Xu was previously a professor at UC San Diego, where the majority of the research was conducted.

The study’s lead authors are Geonho (Tom) Park, now a postdoctoral scholar at Stanford Medicine, who was a graduate student at UC San Diego when the research was conducted; as well as UC San Diego graduate students Yizhou Bian, Hao Huang and Sai Zhou.

Xu and Park are continuing to develop the ultrasound patch at Stanford Medicine.

“Umbilical artery blood flow is one of the components we look at closely when we’re concerned about foetal well-being in cases of placental insufficiency,” said Jane Chueh, an obstetrician at Stanford Medicine, who will be collaborating with Xu’s team on further validation of the technology. But getting the data now is complex, she added.

Current diagnostic tools usually show foetal status in small snapshots of time. Not only does measuring blood flow on existing Doppler ultrasound machines capture data from short windows of time, but it requires a trained ultrasound technician and an appointment, Chueh said, complicating matters even for hospitalised patients.

Another option for evaluating foetal well-being is cardiotocography, a combined measure of foetal heart rate and uterine contractions, data gained from a monitor strapped to the belly.

“It’s really hard to be on that continuously,” Chueh said, noting that the equipment can give false signals or no signals when the foetus is moving a lot. “Even for inpatients, obtaining accurate readings three times a day can be labour intensive.”

In developing the patch, the researchers had to overcome a number of obstacles. Unlike most wearable devices, which measure information at or near the body’s surface, this ultrasound patch needs to collect and interpret information from deep inside the uterus.

Also, everything they hoped to visualise is moving. Not only does the pregnant patient’s body move, but the foetus practices its flip-turns, and the umbilical cord floats freely in the amniotic fluid. In a traditional Doppler ultrasound setup, a technician can reposition the machine’s transducer to get a better view. The researchers used a combination of strategy and technological innovation to tackle the problems.

“We thought what if we target the ultrasound device onto the placenta, in the area where the umbilical cord attaches,” Park said. “Even though everything is moving, there is some stability in the umbilical cord at that location.”

The team developed an image-segmentation algorithm that can track the placenta-anchored end of the umbilical cord in real time, a key element of their design. After developing a prototype and testing it functioned as expected on a simulation mannequin, the researchers ensured it would not deliver too much acoustic or mechanical energy to a foetus. The device meets safety thresholds set by the US Food & Drug Administration, the American Institute of Ultrasound in Medicine and the British Medical Ultrasound Society.

The team tested the patch on 62 pregnant women, comparing its findings with those from a standard Doppler ultrasound machine. The new patch and the traditional machines produced statistically equivalent results.

During the device validation, the research team saw something unexpected in one research participant.

“She was 28 weeks along in her pregnancy – still pretty early on – and an initial examination showed a normal foetal heart rate,” Park said. “Then I saw that the flow signal was quite abnormal. I thought perhaps there’s something malfunctioning in the device, so I checked everything, but it seemed like the device was fine. I showed the data to the physicians who were there, and they agreed that the foetus might be in jeopardy.”

Follow-up testing confirmed that the participant had a severe placental dysfunction. She was monitored closely by her physicians, and the baby was delivered by C-section four days later. The baby went to the neonatal intensive care unit and did well.

The research team plans to refine and validate use of the ultrasound patch at Stanford Medicine (med.stanford.edu). In addition to building a wireless version of the device, they plan to test it in a wider range of patients with other pregnancy complications that involve poor blood flow, such as congenital heart disease and chronic hypertension.

The research paper can be found at www.nature.com/articles/s41587-026-03140-1.