Listening to the Heartbeat, Missing the Breath

During labor, the critical concern is whether the fetus is receiving adequate oxygen. Fetal hypoxia — insufficient oxygen supply due to umbilical cord compression, placental dysfunction, or uterine hyperstimulation — can cause brain injury, cerebral palsy, or death within minutes. The standard monitoring tool is cardiotocography (CTG), which tracks fetal heart rate patterns and uterine contractions, but CTG has a false-positive rate exceeding 60% for predicting fetal acidemia. This means the majority of emergency cesarean sections triggered by concerning fetal heart rate patterns are performed on babies who are not actually in distress. No non-invasive technology can directly measure fetal blood oxygenation through the maternal abdomen during labor.

Approximately 140 million births occur worldwide each year. Intrapartum hypoxia causes an estimated 600,000 neonatal deaths and 1 million cases of neonatal encephalopathy annually, primarily in low-resource settings. In high-resource settings, the primary consequence is unnecessary intervention: the U.S. cesarean section rate is 32% (vs. 10–15% recommended by WHO), driven largely by defensive obstetric practice in response to non-reassuring but non-specific CTG patterns. Each unnecessary cesarean increases maternal morbidity (surgical complications, longer recovery, future pregnancy risks) and costs the healthcare system an estimated $28,000 per case.

CTG has been the standard of care since the 1970s and has not improved neonatal outcomes compared to intermittent auscultation, primarily because of its high false-positive rate. Fetal scalp blood sampling can directly measure fetal blood pH/lactate but is invasive (requires cervical dilation and membrane rupture), intermittent (not continuous), and rarely performed outside of European centers. Fetal pulse oximetry was developed in the early 2000s but the only FDA-approved device (Nellcor FS-14) was withdrawn from the market after clinical trials showed it did not reduce cesarean section rates — the sensor required internal placement on the fetal scalp after membrane rupture, was unreliable during contractions, and clinicians did not trust or change management based on its readings. STAN (ST segment analysis of the fetal ECG) showed promise in Scandinavian trials but failed to demonstrate benefit in a large U.S. trial, possibly because the technology required expertise in interpretation that generalist obstetricians lacked.

A non-invasive, continuous monitoring technology that can quantify fetal cerebral oxygenation through the maternal abdomen during labor — providing a direct measure of the variable that matters (brain oxygen supply) rather than an indirect proxy (heart rate patterns). Candidate technologies include transabdominal near-infrared spectroscopy (but light scattering through maternal tissue severely limits fetal signal); transabdominal photoacoustic imaging (combines optical absorption with ultrasound resolution); or advanced signal processing of fetal ECG waveform morphology that extracts oxygenation-correlated features. Any solution must work during uterine contractions (when monitoring is most critical), on mothers of all body habitus, and be interpretable by labor and delivery nurses and obstetricians with minimal training.

A student team could develop and test a Monte Carlo photon transport model of near-infrared light propagation through layered maternal tissue (skin, fat, uterine wall, amniotic fluid) to quantify the theoretical depth limit and signal-to-noise ratio for transabdominal fetal pulse oximetry. An engineering team could prototype a multi-wavelength photoacoustic sensor array and test its ability to detect oxygenation changes in a tissue phantom at fetal depths. Relevant disciplines: biomedical engineering, biomedical optics, signal processing, obstetrics.