Background: Current methods for assessing perinatal hypoxic conditions did not improve infant outcomes. Various waveform-based and interval-based ECG markers have been suggested, but not directly compared. We compare performance of ECG markers in a standardized ovine model for fetal hypoxia. Methods: Sixty-nine fetal sheep of 0.7 gestation had ECG recorded 4 h before, during, and 4 h after a 25-min period of umbilical cord occlusion (UCO), leading to severe hypoxia. Various ECG markers were calculated, among which were heart rate (HR), HR-corrected ventricular depolarization/ repolarization interval (QT c ), and ST-segment analysis (STAN) episodic and baseline rise markers, analogue to clinical STAN device alarms. Performance of interval-and waveform-based ECG markers was assessed by correlating predicted and actual hypoxic/normoxic state. results: Of the markers studied, HR and QT c demonstrated high sensitivity (≥86%), specificity (≥96%), and positive predictive value (PPV) (≥86%) and detected hypoxia in ≥90% of fetuses at 4 min after UCO. In contrast, STAN episodic and baseline rise markers displayed low sensitivity (≤20%) and could not detect severe fetal hypoxia in 65 and 28% of the animals, respectively. conclusion: Interval-based HR and QT c markers could assess the presence of severe hypoxia. Waveform-based STAN episodic and baseline rise markers were ineffective as markers for hypoxia. c ontinuous monitoring of the fetal heart rate (HR) is assumed to provide clinical information about the wellbeing of the fetus (1). Cardiotocography (CTG) allows noninvasive real-time assessment of fetal HR and its response to uterine contractions and is nowadays used in clinics worldwide. However, HR patterns in CTG are often not predictive for hypoxia (2). Introduction of CTG in clinics did not significantly reduce occurrences of neonatal death or cerebral palsy but did lead to an increase in caesarean sections (1). Consequently, analysis of the ECG ST waveform (STAN) was proposed as an additional analysis method. STAN assesses hypoxia-induced changes in the ST waveform of the ECG (3) and operates in conjunction with CTG. Implementation of STAN in clinical practice was initially associated with a beneficial reduction in hypoxia-induced outcomes (metabolic acidosis and moderate/ severe neonatal encephalopathy) compared to CTG alone (4). However, recent meta-analyses of clinical trials demonstrated no clear advantage of STAN with CTG over CTG alone with respect to primary outcomes (5,6).STAN markers are based on the shape of the ECG waveform. Other ECG markers for hypoxia detection have been suggested, namely, atrioventricular (AV) conduction delay (PR) (7,8), the relationship of AV delay and HR (PR/RR and PR-HR) (9,10) and ventricular activation and repolarization (QT) (11) and HR-corrected QT (QT c,Bazett and Qt c,Hodges ), as well as heart rate variability (HRV) in the temporal and frequency domain. These markers are all interval-based, i.e., they use time intervals between characteristic points in the ECG. A major di...