Transabdominal fetal oximetry, or TFO, device (Daniel Fong, University California in Davis)
18 June 2020. A university engineering lab created a device that safely monitors a fetus’s blood oxygen levels from outside the mother’s abdomen, which could reduce the rate of cesarean sections. A team from University of California in Davis describes the device and tests with animals in the 9 June issue of IEEE Transactions on Biomedical Engineering (paid subscription required), and started a company to commercialize the technology.
Researchers from the Laboratory for Embedded and Programmable Systems, or Leaps, at UC Davis, led by electrical engineering professor Soheil Ghiasi, are seeking better ways to measure blood oxygen concentrations in late-term fetuses. For humans already born, a simple pulse oximeter clipped on a finger or toe sends a beam of light through the skin to detect changes in oxygen saturation from blood hemoglobin based on absorption and reflection of the light.
Obstetricians today need that same information on oxygen levels to monitor the health of the fetus, particularly oxygen deprivation, but lack direct access to the fetus. As a result, those judgments are made with indirect measures, such as fetal heart rate or rate of contractions, which can lead to more cesarean sections than needed if abnormalities are detected. Detecting blood oxygen concentrations from outside the mother’s body is also complicated by more layers of tissue for light beams to cross before reaching the fetus, and weaker signals from the fetus returned to the reading device.
“We wondered if we could build a device to measure fetal blood oxygen saturation directly,” says Ghiasi in a university statement. A Leaps lab team designed a device called the transabdominal fetal oximeter for this task. The device needs to not only send optical beams and read pulse oximetry through multiple layers of tissue, it also needs to distinguish between blood oxygen readings from the fetus and the mother.
The transabdominal fetal oximeter has a patch with infrared transmitters and optical sensors placed on the mother’s abdomen. The device measures reflection and absorption of light from hemoglobin to capture photoplethysmograph or PPG signals indicating changes in blood flow and oxygen saturation. Statistical analysis and filtering of returning PPG signals enable the device distinguish between readings from mother and child.
In the IEEE Transactions paper, and an earlier conference presentation, Ghiasi and colleagues tested the transabdominal fetal oximeter, or TFO, with a pregnant sheep nearing birth. The researchers were able to alter blood flow in the mother with a balloon catheter in an artery, which changed blood oxygen concentrations in the lamb, and measure oxygen levels with both a TFO on the sheep’s abdomen and a pulse oximeter attached the lamb. The results show TFO device readings strongly correlate with pulse oximeter readings from the fetus, as well as discriminate between readings from mother and lamb.
The university applied for patents on the TFO device. In addition, Ghiasi and doctoral candidate Daniel Fong started the company Storx Technologies in Davis earlier this year to take the technology to market. In May, Storx Technologies received a Small Business Technology Transfer award from National Science Foundation to develop a working prototype of the TFO device.
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