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Table 1 Descriptive summary of studies included in review

From: A systematic review of cardiac time intervals utilising non-invasive fetal electrocardiogram in normal fetuses

Characteristics Abboud et al. Taylor et al. Chia et al. Taylor et al. Hayashi et al. Arya et al. Yilmaz et al. Wacker-Gussman. et al.
Study design and methods
 Year of Publication 1990 2003 2005 2005 2009 2015 2015 2017
 Study design Cross sectional study Cross sectional study Prospective cohort study Cross sectional study Cross sectional study Cross sectional study Prospective observation cohort study Cross sectional study
 Inclusion criteria None reported Random sampling Healthy women and fetuses only Women in labour or threatened labour None reported Referred for fetal echocardiography Fetuses with normal cardiac anatomy or CHD Healthy fetuses only
 Gestational Age [weeks] 32 to 41 15 to 41 18 to 41 24 to 41 32 to 41 16 to 42 20 to 38 32 to 40
 Time interval examined PR, QRS, QT PR, QRS, QT, QTc P, PR, QRS, QT, T PR, PQ, QRS, QT, QTc P, QRS, T PR, QRS, RR, QT PR, QRS, QT PR, PQ, QRS, QT, QTc
 Number of patients Not described 241 100 15 48 50 92 149
 Number of acquired FECG 21 250 374 15 48 60 177 149
Signal acquisition
 Number of electrodes 2 14 3 14 5 5 5 5
 Electrodes placement Not described 12 evenly over abdomen, 1 ground ref. near navel, 1 common ref. on right ankle Equilateral triangle formation: 1 right + 1 left hypochondriac area, 1 above symphysis pubis 12 evenly over abdomen, 2 references near umblicus 2 higher abdomen (right/left), 2 lower abdomen (right/left), 1 at distinct fetal heart sound location 2 along midline, 2 at each side of uterus, 1 on left flank 2 along midline, 2 at each side of uterus, 1 on left flank 2 along midline, 2 at each side of uterus, 1 on left flank
 Dermabrasion & impedance None described Yes (< 5 kΩ) Yes(< 5 k Ω) Yes (< 5 kΩ) None reported Yes Yes Yes
 Reported difficulty in signal acquisition None reported Between 27 and 36 weeks Between 27 and 32 weeks None reported None reported Between 26 and 30 weeks Between 24 and 34 weeks Lowest at 32 weeks
Signal processing
 FECG analysed 21 199 374 12 35 20 132 117
 Signal averaging for analysis 100 beats 1 min 2.5 min 1 min 300–500 beats 1 min yes - not described 1000 beats
 Digital filters 4-pole Butterworth non-recursive 10 Hz Highpass 1–2 Hz Highpass, 150 Hz lowpass 1st & 2nd derivative template removal 1 Hz Highpass, 150 Hz Low pass 0.5 Hz low-level an 25 Hz high level removal [0.5–70 Hz] Butterworth bandpass Automated with Monica DK V1.8 software Not reported
 MECG removal Digital subtraction of averaged signal See Patent appl. GB2002/004410 Template subtraction See Patent appl. GB2002/004410 Template subtraction Template matching and digital subtraction Automated with Monica DK V1.8 software Template subtraction
 Success rates in CTI detection QT-80% P,Q, R, S-100%; T-78% P-74.6%, QRS-91.0%, T-79.3% P, QRS-100%, T-92% 72.9% 100% due to strict FECG excl. Criteria PR-77%, QRS-98%, QT-30% P, PQ, PR-97%, QRS-100%, T-41%
  1. CTI Cardiac time intervals, FECG fetal electrocardiogram, MECG Maternal electrocardiogram