In a clever adaptation, a team of researchers developed a fetal monitor using commercial motion sensors to pick up the movement of a pregnant woman’s belly, produced by the heartbeat of the baby or by the baby’s movements in the womb. This early-warning system could potentially prevent about 2.6 million stillbirths around the world.
These sensors are designed to re-orient the displayed image on a smartphone when it is rotated to a horizontal or vertical position. However, the scientists at Stevens Institute of Technology used them to develop a continuous fetal monitoring device that is extremely safe and non-invasive, while offering much greater accuracy than any currently available monitor.
In many pregnancies that end in stillbirths (death of the baby in the womb), the period just before the baby dies is marked by significant changes in the baby’s heart rate and pattern of movement. The ability to reliably detect these changes could provide the crucial window of time necessary to rescue the baby in distress by an immediate delivery or other emergency intervention. The ideal monitor would be light and inexpensive as well as dependable, and the current device fulfils all these criteria.
The wearable Stevens monitor is superior to conventional fetal heart rate monitors in many ways. For one, the latter use electrocardiography (ECG, recordings of the baby’s heart rate) or Doppler ultrasound to pick up the baby’s heartbeat, both of which are expensive technologies. The use of ultrasound for long periods could also cause tissue heating, which could potentially harm the baby. Such equipment is also too large to carry around at times (one system on the market weighs about 11 pounds), and needs to be operated by properly trained personnel.
In comparison, the abdominal Stevens sensors are only one-fifth of an inch in dimension. Again, conventional systems have batteries that last for about 4 hours in contrast to the current device that can use a 3V battery for more than 24 hours. Furthermore, the Stevens vibration monitor passively picks up vibrations rather than emitting or reflecting any form of energy.
The vibration monitor was based on earlier work by researcher Chenxi Yang, who detected the adult heartbeat using chest vibrations. The current project was much more difficult because the baby’s heartbeat is deep inside the mother’s belly, and muted by the mother’s movements as well. Thus the team devised a three-sensor system that picked up signals (including seismocardiograms and gyrocardiograms) from three points, and then identified the fetal heartbeat using algorithms. These sensors record vibrations from inertial sensors attached to the mother’s belly.
The performance of the device was tested on 10 pregnant women in three different positions: lying down, supine and standing. The output was the fetal heartbeat. When this was compared to the heart beat acquired by fetal cardiotocography, based on Doppler ultrasound, the reliability was found to be quite comparable. The supine position was found to be the best.
Another advantage of the vibration monitor is its ability to measure fetal movements without the mother’s active participation. At present, kick counts are recommended, in which the pregnant woman is expected to count the number of movements they feel. This is unreliable in many cases, and overtly reduced fetal movements are a very late sign of fetal distress.
In contrast, being able to assess fetal heart rate and movement together could be an amazing leap forward in ruling out fetal distress. These sensors can also detect fetal movements using the same set-up. Such a monitor would be better than any currently available device, say the researchers, who plan to develop a single monitor that provides both types of information.
The current device is only a proof-of-concept, say the team. While commercially available sensors are used in the current monitor, they plan to build and patent their own sensor. The market for fetal monitors, which are currently based on ECG or ultrasound systems, is expected to cross $ 3.6 billion by 2022. The research team looks forward to making huge inroads in this market.
Researcher Negar Tavassolian comments, “Almost a third of stillbirths occur in the absence of complicating factors. Our device could let a pregnant woman know if her fetus is compromised and she needs to go to the doctor. Our monitors are completely passive, so there's no health concern.”
The study was published in the journal IEEE Sensors Journal on July 24, 2019.
C. Yang, C. Antoine, B. K. Young and N. Tavassolian, "A Pilot Study on Fetal Heart Rate Extraction from Wearable Abdominal Inertial Sensors," in IEEE Sensors Journal. doi: 10.1109/JSEN.2019.2930886, URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=8771190&isnumber=4427201