Fetal ST segment heart rate analysis in labor: improvement of intervention criteria using interpolated base deficit.
OBJECTIVE
The addition of ST waveform analysis (STAN, Neoventa, Sweden) to fetal heart rate (FHR) tracings has been demonstrated to improve fetal outcome and reduce operative delivery rates, though the actual level of fetal acidosis at which STAN indicates intervention has not been assessed. We sought to determine if FHR ST segment analysis recommends intervention at appropriate levels of fetal acidosis.


METHODS
FHR tracings of 10 acidotic and 10 non-acidotic infants with FHR tracings having a minimum of one STAN flag were retrospectively analyzed. Fetal base deficit (BD) was calculated by interpolation throughout the FHR tracing and STAN 'action' and 'ignore' flags assigned a fetal BD value. A secondary analysis was performed with a revised interpretation of FHR reassuring status.


RESULTS
The mean (+/-SD) BD of the first STAN action was significantly greater than the first 'ignore' (4.0+/-2.1 vs. 3.0+/-0.8 mmol/L, p<0.05). Clarified STAN criteria for reassuring vs. non-reassuring FHR resulted in a first action BD of 6.0+/-2.0 mmol/L with 90% sensitivity and 100% specificity for prediction of fetal acidosis.


CONCLUSIONS
The STAN monitor discriminates increasing levels of fetal BD. With clarification of the criteria for reassuring FHR, the calculated BDs of action flags are an appropriate threshold for emergent intervention, successfully predict acidotic fetuses, and avoid unnecessary intervention.
Mansano
Roy Z
RZ
Department of Obstetrics and Gynecology, Harbor-UCLA Medical Center, Torrance, California 90509, USA. rmansano@obgyn.humc.edu
Beall
Marie H
MH
Ross
Michael G
MG
D000138:Acidosis / Q000175:diagnosis* / Q000503:physiopathology; D002585:Cesarean Section / Q000706:statistics & numerical data; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D005316:Fetal Distress / Q000175:diagnosis*; D005323:Fetal Monitoring / Q000379:methods*; D006340:Heart Rate, Fetal / Q000502:physiology*; D006801:Humans; D011247:Pregnancy; D011256:Pregnancy Outcome; D012189:Retrospective Studies