Early detection of postpartum hemorrhage can save lives with simple, low-cost interventions.
In the delivery room, a seemingly routine birth can become critical in an instant if a patient begins losing large amounts of blood.
A mother can appear stable one moment, and then experience a rapid drop in vital signs, requiring urgent interventions such as a blood transfusion or emergency surgery. ()
The Challenge of Timely Postpartum Hemorrhage Detection
Postpartum hemorrhage is a leading cause of maternal deaths worldwide, yet it can be difficult to detect in time. Patients often do not notice the bleeding themselves, and even experienced medical staff cannot accurately gauge blood loss by visual observation alone.
Christine O’Brien, an assistant professor of biomedical engineering at Washington University in St. Louis, notes that existing methods, like counting blood-soaked sponges or using calibrated collection drapes, may seem basic but remain some of the most reliable ways to identify excessive bleeding. She estimates that a continuous, accurate monitoring system, combined with prompt treatment, could prevent between 50% and 90% of maternal deaths caused by hemorrhage.
Blood loss is “difficult to measure and if you wait on normal vital signs like heart rate or blood pressure. Those can remain stable for up to 1,500 milliliters of blood loss,” she said. (Postpartum hemorrhage is classified as blood loss of at least 1 liter, or 1,000 milliliters, within 24 hours of birth).
Tracking drops in blood pressure also won’t necessarily provide the right data because modern delivery rooms are constantly adding medications and fluids to the patient that might affect that measurement.
Instead, O’Brien, with a five-year $2.8 million grant from the National Heart, Lung, and Blood Institute, a part of the National Institutes of Health (NIH), aims to develop a wearable device that tracks blood loss through measuring cardiovascular features from a novel light-based sensor that measures changes in hemoglobin and blood flow.
Analyzing Cardiovascular Waveforms for Early Hemorrhage Detection
This measurement produces waveforms based on how the heart is pumping and how the rest of circulatory system resists that flow. The shape of those waveforms changes based on the state of a person’s cardiovascular system. Using statistical and machine-learning algorithms, they can determine which features of the waveforms are correlated with absolute blood loss.
With an affordable wearable device that fits on a wrist and tracks blood flow, “we’ll be able to have a much clearer signal when someone is hemorrhaging,” O’Brien said.
The device will be tested on animal models with differently pigmented skin to ensure skin color does not impact the sensor readout. In devices that run on light-based sensors, like pulse oximeters, skin color can affect the accuracy of the blood oxygen-level measurements.
Skin tone shouldn’t impact reading of this new light-based sensor’s waveforms, but they’ll be testing it nonetheless in both preclinical models and in a diverse mix of human test subjects to ensure the sensor works correctly under differing circumstances. That also includes testing it on subjects with varying levels of hemodilution (hemoglobin being watered down by other fluids).
Though they are working on a way to track blood loss, the overarching aim is to prevent postpartum hemorrhage, O’Brien said. With early warning, oftentimes simple, low-cost interventions, such as massaging the uterus, could stop the bleeding. Not all hospitals are fully stocked to handle an emergency blood transfusion or surgery, so it’s better not to lose so much blood in the first place.
“You can find yourself in an emergency very quickly,” O’Brien said.
References:
- Tracking the deadly and unpredictable postpartum hemorrhage – (https://engineering.washu.edu/news/2025/Tracking-the-deadly-and-unpredictable-postpartum-hemorrhage.html)
Source-Eurekalert