Wearable Ultrasound Patch Tracks Fetal Blood Flow Hands-Free in High-Risk Pregnancies

For the first time, a wearable ultrasound patch can continuously monitor blood flow in the umbilical cord—without a sonographer—offering a potential new way to catch early signs of fetal compromise in high-risk pregnancies. The device, called UPatch, sticks to the mother’s abdomen and autonomously tracks moving vessels while the mother moves, providing a real-time stream of Doppler indices that reveal how well the placenta is supporting the fetus.

Scientists report the work today in Nature Biotechnology. The study was led by senior author Sheng Xu at the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the University of California, San Diego, with first author Geonho Park.

The team validated the UPatch against a standard handheld clinical ultrasound system in 62 pregnancies. The patch’s measurements of umbilical artery Doppler indices—including the systolic-to-diastolic ratio, pulsatility index, and resistance index—agreed closely with the clinical device, with mean differences all under 1%. Fetal heart rate readings matched within about one beat per minute. The patch also captured standard fetal biometrics like head circumference and femur length used to estimate fetal weight.

A key innovation is an image-segmentation algorithm that identifies pulsating blood vessels in duplex ultrasound images and automatically places a sample gate for Doppler measurement. In tests, the algorithm’s gate placement matched a sonographer’s within 2 mm in more than 90% of cases and was considered accurate by sonographers in over 91% of UPatch images. This tracking allows continuous collection of blood flow spectra even as the fetus moves, without manually repositioning the probe.

In a continuous monitoring study of 52 pregnant women—including healthy participants and those with conditions such as preeclampsia, gestational hypertension, gestational diabetes, and fetal growth abnormalities—the UPatch revealed striking patterns. Fetal heart rate alone could not discriminate between healthy and complicated pregnancies; the distributions overlapped substantially. In contrast, Doppler indices showed clear differences. For example, in a preeclamptic participant, the patch recorded absent end-diastolic flow nearly 25% of the time and markedly elevated pulsatility and resistance indices, leading to intensified monitoring and delivery by Cesarean section four days later.

Critically, continuous monitoring also revealed transient fluctuations that temporarily pushed Doppler indices into an abnormal range. These bursts, which would likely go unnoticed with snapshot clinical scans, could be misinterpreted as persistent pathology. The UPatch’s uninterrupted data stream provides the temporal context to separate such harmless variations from sustained compromise, potentially reducing unnecessary interventions.

The study is a prospective, device-validation and observational cohort investigation. Several limitations remain. The patch is currently wired to a bulky backend system, limiting mobility to inpatient settings. The autonomous tracking algorithm pauses spectral acquisition to locate the vessel again when the cord moves quickly, causing brief signal interruptions. The research team notes that future work will integrate wireless circuits, enable simultaneous tracking and measurement, and combine fetal data with maternal physiological signals.

As the technology matures, continuous, hands-free monitoring could extend high-quality fetal surveillance beyond specialized centers, particularly in low-resource settings where sonographers are scarce and pregnancy complications remain high. Larger studies will be needed to confirm whether this approach can reliably guide clinical decisions and improve outcomes.

Reference: Park, G., Bian, Y., Huang, H. et al. Fetal monitoring for high-risk pregnancies using a wearable ultrasound patch. Nat Biotechnol (2026). https://doi.org/10.1038/s41587-026-03140-1