listening to the

heartbeat, missing the breath

Problem statement

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.

Why this matters

Approximately 140 million births occur worldwide each year (WHO). Intrapartum-related hypoxic events caused an estimated 510,000–717,000 neonatal deaths and roughly 1.15 million new cases of neonatal encephalopathy in 2010, 96% of them in low- and middle-income countries (Lee et al. 2013). In high-resource settings, the primary consequence is unnecessary intervention: the U.S. cesarean section rate was 32.3% in 2023 (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 cost: average commercial-insurer payments for maternal and newborn care ran $27,866 for cesarean births vs. $18,329 for vaginal births (Truven Health Analytics 2013).

What’s been tried and why it hasn’t worked

CTG has been the standard of care since the 1970s, but the Cochrane review found it has not reduced perinatal mortality or cerebral palsy compared to intermittent auscultation (it does roughly halve neonatal seizures) while significantly increasing cesarean deliveries (Alfirevic et al. 2017). 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 late 1990s–2000s, but the only FDA-approved system (Nellcor's OxiFirst — the N-400 monitor with FS-14 fetal sensor, conditionally approved in 2000) was pulled from the market by its manufacturer after a 5,341-woman NICHD trial found that displaying fetal oxygen saturation neither reduced cesarean delivery rates nor improved newborn condition (Bloom et al. 2006) — the sensor required internal placement against the fetus after membrane rupture, was unreliable during contractions, and knowledge of its readings did not change management outcomes. STAN (ST segment analysis of the fetal ECG) showed promise in Scandinavian trials but failed to demonstrate benefit in a large U.S. trial of 11,108 women (Belfort et al. 2015), possibly because the technology required expertise in interpretation that generalist obstetricians lacked.

What would unlock progress

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.

Entry points for student teams

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.