Each year in the U.S., there are about 24,000 stillbirths — about 1% of all births — according to the CDC. Medical science does not know all the reasons for stillbirth, says Stevens Institute of Technology associate professor Negar Tavassolian. About a third of all stillborn babies have no known complicating factors although heartbeat and movement variations often precede stillbirths, according to the Tavassolian and Chenxi Yang, a Stevens graduate student. The Stevens researchers developed a sensor that detects vibrations transmitted through the mother’s abdomen with fetal heartbeats and when a fetus moves.

In a study published in IEEE Sensors Journal, Tavassolian and Yang reported on the ability of their device to alert mothers to signs of distress with their babies in the last weeks of pregnancy. The device uses the same sensors used to sense vertical and horizontal orientation in smartphones.

Unlike ultrasound monitors, which can heat tissue with continuous use, the Stevens vibration sensor is passive. It only reads signals transmitted naturally and does not affect the baby or the mother. Conventional heartbeat monitors are heavy, expensive, have short battery life, and require specialized training. The Stevens design, however, which uses three sensors to isolate the fetal heartbeat vibrations from the mother’s movements, is about one-fifth of an inch long, weighs very little, and can run for more than a day with a 3-volt battery.

Based on their experiments with ten pregnant women in conjunction with their OB-GYNs at New York University’s Longone Medical Center, the Stevens researchers reported their vibration monitor measured fetal heartbeats with accuracy equivalent to fetal cardiocograms (f=CTG), the current gold standard.

The next steps for Yang and Tavassolian include patenting and marketing a custom-built wearable sensor.