Phase-rectified signal averaging for intrapartum electronic fetal heart rate monitoring is related to acidaemia at birth.
OBJECTIVE
Recent studies suggest that phase-rectified signal averaging (PRSA), measured in antepartum fetal heart rate (FHR) traces, may sensitively indicate fetal status; however, its value has not been assessed during labour. We determined whether PRSA relates to acidaemia in labour, and compare its performance to short-term variation (STV), a related computerised FHR feature.


METHODS
Historical cohort.


METHODS
Large UK teaching hospital.


METHODS
All 7568 Oxford deliveries that met the study criteria from April 1993 to February 2008.


METHODS
We analysed the last 30 minutes of the FHR and associated outcomes of infants. We used computerised analysis to calculate PRSA decelerative capacity (DC(PRSA)), and its ability to predict umbilical arterial blood pH ≤ 7.05 using receiver operator characteristic (ROC) curves and event rate estimates (EveREst). We compared DC(PRSA) with STV calculated on the same traces.


METHODS
Umbilical arterial blood pH ≤ 7.05.


RESULTS
We found that PRSA could be measured in all cases. DC(PRSA) predicted acidaemia significantly better than STV: the area under the ROC curve was 0.665 (95% CI 0.632-0.699) for DC(PRSA), and 0.606 (0.573-0.639) for STV (P = 0.007). EveREst plots showed that in the worst fifth centile of cases, the incidence of low pH was 17.75% for DC(PRSA) but 11.00% for STV (P < 0.001). DC(PRSA) was not highly correlated with STV.


CONCLUSIONS
DC(PRSA) of the FHR can be measured in labour, and appears to predict acidaemia more accurately than STV. Further prospective evaluation is warranted to assess whether this could be clinically useful. The weak correlation between DC(PRSA) and STV suggests that they could be combined in multivariate FHR analyses.
Nuffield Department of Obstetrics & Gynaecology, University of Oxford, Women's Centre, John Radcliffe Hospital, Oxford, UK; Department of Engineering Science, Institute of Biomedical Engineering, University of Oxford, Oxford, UK.
A
A
Georgieva
A T
AT
Papageorghiou
S J
SJ
Payne
M
M
Moulden
C W G
CW
Redman
D000138:Acidosis / Q000097:blood* / Q000503:physiopathology*; D015148:Cardiotocography; D015331:Cohort Studies; D005260:Female; D005315:Fetal Diseases / Q000503:physiopathology; D006340:Heart Rate, Fetal / Q000502:physiology*; D006801:Humans; D011247:Pregnancy; D012189:Retrospective Studies
Decision support; electronic fetal monitoring; phase-rectified signal averaging; sensitivity and specificity; short-term variation