Table 1 Descriptive summary of studies included in review
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% |