Turning Smartphones into Lifesaving Fetal Monitors
Professor Alexander Adams runs the Uncommon Senses lab out of Tech Square’s TSRB building. The lab focuses on the design, fabrication, and implementation of new wearable sensing systems. Adams’s current research focuses on equity-driven design and multi-modal sensing systems in the realms of mental and physical health.
When Georgia Tech professor Alexander T. Adams (Uncommon Sense Labs, College of Computing) and his wife endured two miscarriages, he saw firsthand the gaps in fetal monitoring and maternal health. Even during a later successful pregnancy, using an at-home Doppler fetal monitor proved challenging. “It was hard for my wife to use the commodity Doppler. I ended up having to use it for her,” Adams recalls, noting that such devices require precise positioning, technical skill, and calm under stress to find a heartbeat. Existing at-home fetal heart rate (FHR) monitors are “quite dumb” devices and lack any contextual information, he says. “While they can work, their accuracy is good if you get it just right, but it requires some skill and definitely requires you not to panic.”
Those limitations inspired Adams to look for an alternative. He set out to leverage something nearly every expectant parent already owns: a smartphone.
DopFone: A Doppler Heartbeat Monitor in Your Phone
Adams’s solution, developed with collaborators at the University of Washington, is called DopFone, a system that turns an ordinary smartphone into a fetal heart monitor. DopFone uses the phone’s built-in speaker and microphone as a makeshift Doppler ultrasound. The phone emits an 18-kilohertz ultrasonic tone (inaudible but just beyond human hearing) and listens for subtle reflections from the abdomen. Each tiny vibration from the fetal heartbeat slightly shifts the reflected sound frequency, creating a Doppler effect. By analyzing those faint audio signals, DopFone’s algorithms can estimate fetal heart rate without probes, gel, or external hardware.
Paired with a machine-learning model, DopFone estimates fetal heart rate during a roughly 60-second session by simply placing a smartphone on the abdomen. In a clinical study involving 23 pregnant participants, the system’s readings closely matched those of a medical-grade Doppler device, with an average error of about 2 beats per minute, which is well within the ±8 BPM margin considered clinically acceptable by physicians. The results place DopFone on par with standard prenatal Dopplers, which typically cost thousands of dollars.
Promising Results Across Gestation and Body Types
One unexpected advantage of using a smartphone is flexibility. Traditional fetal Dopplers rely on focused, high-frequency ultrasound that produces a strong signal only when precisely aimed at a small area. DopFone uses a much lower frequency, creating a larger acoustic wave. “We get a worse signal, but better all around, if that makes sense,” Adams says. While the lower-frequency ultrasound cannot pinpoint the fetal heart as sharply, it also does not drop out when the phone shifts slightly.
The study tested participants between 19-39 weeks of gestation and found only minor differences in performance across pregnancy stages. The most significant factor affecting accuracy was maternal body mass index (BMI). In higher-BMI cases early in pregnancy, error could rise to around eight BPM, largely because the fetus is smaller and farther away behind more tissue. “That’s kind of the edge case,” Adams says, adding that similar limitations affect all fetal monitoring technologies.
Because DopFone is software-based, it can account for some of these challenges by incorporating inputs such as gestational age and maternal weight. In practice, the app can explain when conditions, such as fetal position or tissue depth, make it harder to detect a heartbeat. Even with these variables, DopFone delivered reliable readings across a diverse cohort, remaining robust across gestational ages, BMIs ranging from 23 to 67, and varied phone placements. In 95 percent of cases, estimates fell within about 5 BPM of the medical reference device.
Bridging Gaps in Prenatal Care Access
The implications of a phone-based fetal monitor extend beyond technical performance. Fetal heart rate monitoring is a standard part of prenatal care, typically conducted during clinic visits or continuous hospital monitoring during labor. But traditional equipment is expensive and requires trained personnel, leaving many patients in rural or low-resource settings without frequent assessments. Missed warning signs can have tragic consequences. The World Health Organization estimates that roughly two million stillbirths occur worldwide each year, many of them preventable with timely care. In the United States, about 21,000 families experience stillbirth annually, with rural communities and groups that have been historically marginalized facing elevated risk.
By turning a ubiquitous consumer device like a smartphone into a medical tool, DopFone aims to expand access to fetal health monitoring. “If we can get something to work on a smartphone, our ability to become ubiquitous is increased a thousand-fold,” Adams says. With nearly five billion smartphone users worldwide, including people in medically underserved regions, a tool like DopFone could bridge the gap between clinic-based monitoring and at-home reassurance. Frequent fetal heart rate monitoring checks may reduce unnecessary hospital visits, empower expectant parents, and flag potential issues earlier.
Adams also sees DopFone as one piece of a broader prenatal health ecosystem. His lab is pairing the fetal heart rate tool with other smartphone-based diagnostics, including a urinalysis test designed to screen for early signs of preeclampsia. Bundling multiple indicators into a single platform could allow a phone to offer a more holistic prenatal check-up, flagging when something looks abnormal and guiding patients toward care. This approach could be especially impactful in states like Georgia, where maternal mortality remains high, and some rural patients live hours from the nearest obstetric hospital. “Early indication to get to a hospital is important,” Adams notes, “because sometimes it’s not a 10- or 15-minute drive.”
In rural communities where prenatal care can be hours away, DopFone points to a future where expectant mothers can check fetal heart rate using a tool they already carry. (Image: Lucas Gallone/Unsplash)
Caution and Next Steps: Toward Safe, Effective Home Use
Despite its promise, DopFone is not designed to replace prenatal visits or clinician expertise. Instead, the researchers frame it as a supplemental tool to fill gaps between appointments. “Our goal is not to replace the current standard of care,” the team writes, “but to develop an accessible alternative for cases when traditional FHR assessments are not readily available.”
Regulatory and practical hurdles remain. Many handheld Dopplers sold online are FDA-approved, but only if used by a professional. Adams encountered regulatory barriers while attempting early clinic testing in Georgia, where use by clinicians would classify the system as a medical device. To move the research forward, the initial clinical study was conducted through the University of Washington’s medical school.
Now, Adams’ team has approval to test DopFone in real-world settings across Atlanta, allowing pregnant volunteers to use the app at home. These studies will evaluate usability, background noise, user movement, and device variability. “We have enough evidence now that this works in ideal settings really well,” Adams says. The next challenge is understanding how it performs outside the clinic.
The team is also refining how results are communicated. Rather than triggering alarms, DopFone may indicate whether readings fall “within a healthy range.” If no clear heartbeat is detected, the app can suggest repositioning and explain why there may be no signal, reducing unnecessary anxiety. “The biggest obstacle,” Adams explains, “is making sure we’re giving information we’re confident about, and that users know how confident we are as well.”
Innovation for Maternal Health Equity
What began as a research project shaped by personal loss has grown into a promising example of how everyday technology can expand access to care. By lowering barriers to fetal monitoring, Adams and his collaborators are exploring how smartphones might democratize a part of prenatal care long confined to clinics, offering reassurance, earlier insight, and potentially better outcomes for mothers and babies alike.