Purpose: Phase-rectified signal averaging method (PRSA) represents an analysis method which applied on fetal cardiotocography (CTG) allows the quantification of the speed of fetal heart rate changes. By calculating the average deceleration capacity (ADC) an assessment of the fetal autonomic nervous system (ANS) is possible. The objective of this study was to test its ability to predict perinatal acidosis.
Methods: A case-control study was performed at a University Hospital in Munich. All intrapartum CTG heart rate tracings saved during a 7-year period were considered for analysis. All neonates born with an umbilical arterial blood pH ≤ 7.10 were considered as cases. Controls were defined as healthy fetuses born with a pH ≥ 7.25. The main matching criteria were gestational age at delivery, parity, birth mode, and birth weight percentile. Exclusion criteria were a planned caesarean section, fetal malformations, and multiple pregnancies. ADC and STV were then calculated during the last 60, the last 45, and the last 30 min intervals prior to delivery.
Results: Of all stored birth CTG recordings, 227 cases met the inclusion criteria and were studied. ADC was significantly higher in fetuses born with acidemia (4.85 bpm ± 3.0) compared to controls (3.36 bpm ± 2.2). The area under ROC curve was 0.659 (95% CI 0.608-0.710) for ADC and 0.566 (0.512-0.620) for STV (p = 0.013).
Conclusions: This study confirms that the assessment of ADC using PRSA represents a good additional tool for the prediction of acute fetal acidosis during delivery.
Keywords: Acute fetal hypoxia; Average acceleration capacity; Average deceleration capacity; Fetal heart rate variability; PRSA; STV.