Phase-rectified signal averaging as a new method for surveillance of growth restricted fetuses

Objective: This study aims to compare average acceleration capacity (AAC), a new parameter to assess the dynamic capacity of the fetal autonomous nervous system, and short term variation (STV) in fetuses affected by intrauterine growth restriction (IUGR) and healthy fetuses. Methods: A prospective observational study was performed, including 39 women with IUGR singleton pregnancies (estimated fetal weight <10th percentile and umbilical artery resistance index >95th percentile) and 43 healthy control pregnancies matched according to gestational age at recording. Ultrasound biometries and Doppler examination were performed for identification of IUGR and control fetuses, with subsequent analysis of fetal heart rate, resulting in STV and AAC. Follow-up for IUGR and control pregnancies was done, with perinatal outcome variables recorded. Results: AAC [IUGR mean value 2.0 bpm (interquartile range = 1.6–2.1), control 2.7 bpm (2.6–3.0)] differentiates better than STV [IUGR 7.4 ms (5.3–8.9), control 10.9 ms (9.2–12.7)] between IUGR and control. The area under the curve for AAC is 97 % [95% CI = (0.95–1.0)], for STV 85 % (CI = 0.76–0.93; p < 0.01). Positive predictive value for STV is 77% and negative predictive value is 81%. For AAC both positive and negative predictive values are 90%. Conclusions: AAC shows an improvement to discriminate between normal and compromised fetuses at a single moment in time, in comparison with STV.