title: Electrocardiography versus photoplethysmography in assessment of maternal heart rate variability during labor.
abstract: OBJECTIVE
  Evaluation of maternal heart rate (MHR) variability provides useful information on the maternal-fetal clinical state. Electrocardiography (ECG) is the most accurate method to monitor MHR but it may not always be available, and pulse oximetry using photoplethysmography (PPG) can be an alternative. In this study we compared ECG and PPG signals, obtained with conventional fetal monitors, to evaluate signal loss, MHR variability indices, and the ability of the latter to predict fetal acidemia and operative delivery.
  
  
  METHODS
  Both signals were simultaneously acquired in 51 term pregnancies during the last 2 h of labor (H1 and H2). Linear time- and frequency-domain, and nonlinear MHR variability indices were estimated, and the dataset was divided into normal and acidemic cases, as well as into normal and operative deliveries. Differences between ECG and PPG signals were assessed using non-parametric confidence intervals, hypothesis testing, correlation coefficient and a measure of disagreement. Prediction of fetal acidemia and operative delivery was assessed using areas under the receiver operating characteristic curve (auROC).
  
  
  RESULTS
  Signal loss was higher with ECG during the first segments of H1, and higher with PPG in the last segment of H2, and it increased in both signals with labour progression. MHR variability indices were significantly different when acquired with ECG and PPG signals, with low correlation coefficients and high disagreement for entropy and fast oscillation-based indices, and low disagreement for the mean MHR and slow oscillation-based indices. However, both acquisition modes evidenced significant differences between H1 and H2 and comparable auROC values were obtained in the detection of fetal acidemia and operative vaginal delivery.
  
  
  CONCLUSIONS
  Although PPG captures the faster oscillations of the MHR signal less well than ECG and is prone to have higher signal loss in the last 10-min preceding delivery, it can be considered an alternative for MHR monitoring during labor, with adaptation of cut-off values for MHR variability indices.
authors.affiliation: Center for Health Technology and Services Research (CINTESIS), Faculty of Medicine, University of Porto, Rua Dr Plácido da Costa, s/n, 4200-450 Porto, Portugal.
authors.forename: Hernâni
authors.initials: H
authors.lastname: Gonçalves
authors.affiliation: Center for Health Technology and Services Research (CINTESIS), Faculty of Medicine, University of Porto, Rua Dr Plácido da Costa, s/n, 4200-450 Porto, Portugal ; Department of Obstetrics and Gynecology, Medical School, University of Porto, Porto, Portugal ; Hospital Dr Nélio Mendonça, EPE, Funchal, Portugal.
authors.forename: Paula
authors.initials: P
authors.lastname: Pinto
authors.affiliation: Department of Obstetrics and Gynecology, Medical School, University of Porto, Porto, Portugal.
authors.forename: Manuela
authors.initials: M
authors.lastname: Silva
authors.affiliation: Department of Obstetrics and Gynecology, Medical School, University of Porto, Porto, Portugal ; Department of Obstetrics and Gynecology, São João Hospital, Porto, Portugal ; INEB - Institute of Biomedical Engineering, Porto; I3S - Institute for Research and Innovation in Health, University of Porto, Porto, Portugal.
authors.forename: Diogo
authors.initials: D
authors.lastname: Ayres-de-Campos
authors.affiliation: Center for Health Technology and Services Research (CINTESIS), Faculty of Medicine, University of Porto, Rua Dr Plácido da Costa, s/n, 4200-450 Porto, Portugal ; Department of Obstetrics and Gynecology, Medical School, University of Porto, Porto, Portugal ; Department of Obstetrics and Gynecology, São João Hospital, Porto, Portugal ; Hospital Pedro Hispano, Unidade Local de Saúde de Matosinhos, Senhora da Hora, Portugal.
authors.forename: João
authors.initials: J
authors.lastname: Bernardes
keywords: Cardiotocography; Electrocardiography; Fetal monitoring; Maternal heart rate; Pulse oximetry; Signal processing