Quantitative assessment of fetal well-being through CTG recordings: a new parameter based on Phase Rectified Signal Average

Cardiotocography (CTG) represents a standard approach to monitor fetal well being during pregnancy. It is based on the simultaneous recording of the fetal heart rate (FHR) signal and uterine contractions. The necessity to reduce inter- and intra-observer variability in the interpretation of CTG tracings has brought researchers to define new parameters to reliably quantify FHR variability. In this paper, a new parameter based on the Phase Rectified Signal Average (PRSA) curve is introduced. The parameter is defined as the slope of the PRSA curve, namely Acceleration Phase Rectified Slope (APRS) or Deceleration Phase Rectified Slope (DPRS), depending on the sign of the slope. The parameter was applied to FHR time series acquired from healthy and IUGR fetuses during a CTG non-stress test. The performance of APRS and DPRS was compared with the performance of other parameters extracted from the PRSA curve already existing in literature, and with other clinical indices that are provided by computerized cardiotocographic systems. The APRS and DPRS performed better than any other parameter considered in this study to distinguish between healthy and IUGR fetuses. We believe that this new index might be useful to improve the quality of fetus early diagnosis.