UC Davis ECE Professor Soheil Ghiasi's Lab Develops Fetal Oximetry Device to Prevent Unneeded C-Sections
The Centers for Disease Control and Prevention reports that more than 31% of all baby deliveries in the U.S. were by C-section in 2018. While some C-sections are necessary, any surgery comes with risks. Therefore, both medical professionals and insurance companies would like to avoid unnecessary C-sections.
Potential fetal hypoxia is one reason surgeons rush in to perform a C-section. Currently, obstetricians assess the baby's well-being using electronic fetal heart rate monitoring (EFM) during labor and delivery. As of 2016, data published in Clinical Obstetrics & Gynaecology showed that 30 percent of babies delivered in hospitals in the U.S. are detected as potentially hypoxic, but 60 percent of those detections are false alarms that can lead to unnecessary C-sections.
UC Davis electrical and computer engineering professor Soheil Ghiasi's lab has built a transabdominal fetal pulse oximeter (TFO) to measure a baby's blood oxygen saturation levels non-invasively. A new father himself, he credits the birth of his young daughter with inspiration for this research, which is supported by grants from the National Science Foundation and the National Institutes of Health.
Ghiasi expects this technology to be adoptable by many medical facilities worldwide.
"From my observations, nurses and obstetricians are well-trained on how to use fetal monitoring devices, and this is something to which they can easily adapt. Placing TFO on the abdomen is similar to placing ultrasound transducers currently used for fetal monitoring at hospitals. A friendly graphical user interface can provide easy access to fetal oxygen saturation numbers outputted by the TFO and help with the adaptation. Additionally, TFO is composed of off-the-shelf components and is relatively low-cost.” - Dr. Soheil Ghiasi
Begum Kasap, a Ph.D. student working on the project, explains the concept behind the TFO technology.
"This works by placing multiple near-infrared LED light sources and a pair of photodetectors on the mother’s abdomen placed at 'near' and 'far' positions. The measured reflected light at the near detector is impacted only by the mother’s tissue layers. The light at the far detector travels through both maternal and fetal tissues. We filter the maternal signal from the far detector's measurement to extract a signal belonging to the fetus using adaptive noise cancellation and the near detector's maternal signal measurement. As a result of filtering, we can identify a PPG signal belonging to the baby which can be used to estimate oxygen saturation.”
Testing Accuracy in Pregnant Ewes
They are currently testing the accuracy of the fetal oximeter in pregnant ewes, in collaboration with Diana L. Farmer, a fetal surgeon at UC Davis Health.
They also collaborated with Herman Hedriana and Aijun Wang at UC Davis Health; Weijian Yang, Naoki Saito, Andre Knoesen, and Vivek Srinivasan at UC Davis; and M. Austin Johnson, previously at UC Davis Health and now at the University of Utah.
"We have done thirteen animal studies with various prototypes of the TFO device since 2019, thanks to all of these collaborators. Our latest animal study showed that our TFO can measure fetal oxygen saturation with about 10 percent mean absolute error," explains Kasap.
Accessing reference oxygen saturation values is necessary to characterize and calibrate any pulse oximetry system. To accomplish this, researchers can draw blood from the sheep fetuses during the study (in a strict protocol, approved by the UC Davis Institutional Animal Care and Use Committee, where the sheep are under anesthesia) to compare actual fetal blood oxygenation data with observations from the TFO technology.
Results from their animal studies were presented at the Society for Maternal-Fetal Medicine pregnancy meeting in January 2021 and at the 43rd Annual International Conference of the IEEE Engineering in Medicine and Biology Society in November 2021.
Prenatal Testing in Humans
This new oximeter was tested on a small group of humans in 2021 in collaboration with Herman Hedriana, director of Maternal-Fetal Medicine at UC Davis Health. Healthy near-term pregnant patients coming in for their non-stress test (NST) visits were enrolled in the study, which was approved by UC Davis' Institutional Review Board and conducted at UC Davis' Medical Center. The evaluation of TFO for use in prenatal testing is an important step towards its integration into hospitals for fetal monitoring during labor and delivery. However, because researchers cannot draw blood as frequently from human fetuses, the performance of TFO in humans is evaluated using proxy metrics, such as fetal heart rate and maternal heart rate.
"We had a mean absolute error of 6.3 beats per minute (bpm) for fetal heart rate with our technology and a mean absolute error of 1.3 maternal heartbeats per minute across three patients. We want an error of below 5 bpm for a clinical application, so we are working on this," says Kasap.
The device has been tested with patients with darker skin tones, and it has proven less accurate than those with lighter skin. "More light gets absorbed while passing through the body of someone with a darker skin tone, so less light is reflected to the surface, making it harder to obtain observations," said Kasap. In order to correct this, they've made it possible to adjust the brightness of the LED light source. However, there's a safety-related upper limit on brightness to avoid the possibility that the LED in contact with someone's body will overheat.
Results from their human studies were presented at the 17th IEEE-EMBS International Conference On Wearable And Implantable Body Sensor Networks in July 2021.
They are developing another prototype that is less sensitive to 'noise' - other things the sensors pick up that have nothing to do with fetal blood oxygenation - which can work with lower levels of light. In this coming year, Ghiasi, Kasap and their many collaborators will carry out further oximeter tests during labor and delivery in both animals and humans.
