Intrapartum non-invasive electrophysiological monitoring: A prospective observational study

Doppler ultrasound cardiotocography is a non-invasive alternative that, despite its poor specificity, is often first choice for intrapartum monitoring. Doppler ultrasound suffers from signal loss due to fetal movements and is negatively correlated with maternal body mass index (BMI). Reported accuracy of fetal heart rate monitoring by Doppler ultrasound varies between 10.6 and 14.3 bpm and reliability between 62.4% and 73%. The fetal scalp electrode (FSE) is considered the reference standard for fetal monitoring but can only be applied after membranes have ruptured with sufficient cervical dilatation and is sometimes contra-indicated. A non-invasive alternative that overcomes the shortcomings of Doppler ultrasound, providing reliable information on fetal heart rate, could be the answer. Non-invasive fetal electrocardiography (NI-fECG) uses a wireless electrode patch on the maternal abdomen to obtain both fetal and maternal heart rate signals as well as an electrohysterogram. We aimed to validate a wireless NI-fECG device for intrapartum monitoring in term singleton pregnancies, by comparison with the FSE.

We performed a multicenter cross-sectional observational study at labor wards of 6 hospitals located in the Netherlands, Belgium, and Spain. Laboring women with a healthy singleton fetus in cephalic presentation and gestational age between 36 and 42 weeks were included. Participants received an abdominal electrode patch and FSE after written informed consent. Accuracy, reliability, and success rate of fetal heart rate readings were determined, using FSE as reference standard. Analysis was performed for the total population and measurement period as well as separated by labor stage and BMI class (≤30 and >30 kg/m² ).

We included a total of 125 women. Simultaneous registrations with NI-fECG and FSE were available in 103 women. Overall accuracy is -1.46 bpm and overall reliability 86.84%. Overall success rate of the NI-fECG is around 90% for the total population as well as for both BMI subgroups. Success rate dropped to 63% during second stage of labor, similar results are found when looking at the separate BMI groups.

Performance measures of the NI-fECG device are good in the overall group and the separate BMI groups. Compared with Doppler ultrasound performance measures from the literature, NI-fECG is a more accurate alternative. Especially, when women have a higher BMI, NI-fECG performs well, resembling FSE performance measures.