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Table 2 The regression equations of Doppler indices as a function of gestational age in weeks

From: Reference values for fetal Doppler-based cardiocirculatory indices in monochorionic-diamniotic twin pregnancy

Doppler index

Transformation

Constant

SD

r2

P-value

95% CI around regression slope coefficients

UA-PI

–

2.441–0.0648GA + 0.0007GA2

0.1981

0.349

< 0.001

− 0.1063 – − 0.0233 for GA

− 0.0001 - 0.0015 for GA2

MCA-PI

–

− 0.325 + 0.1286GA - 0.0021GA2

0.2358

0.169

< 0.001

0.0792–0.178 for GA

− 0.003 - -0.0011 for GA2

CPR

log10

− 0.7936 + 0.0544GA – 0.0007GA2

0.0882

0.45

< 0.001

0.036–0.073 for GA

− 0.0011 - -0.0004 for GA2

MCA-PSV

–

38.4–1.917GA + 0.0647GA2

6.651

0.595

< 0.001

−3.311 – − 0.5235 for GA

0.0387–0.0907 for GA2

DV-PIV

log10

0.2189–0.029GA + 0.0004GA2

0.1156

0.135

< 0.001

− 0.0533 – 0.0048 for GA

− 0.0001 - 0.0008 for GA2

DV-S/a

log10

0.5817–0.0185GA + 0.0002GA2

0.078

0.143

< 0.001

− 0.0349 – − 0.0022 for GA

− 0.0001 - 0.0005 for GA2

DV-E

–

0.0235 + 0.0025GA - 0.00004GA2

0.0101

0.035

< 0.001

0.0004–0.0046 for GA

− 0.00008 - -0.000001 for GA2

MV-E/A

–

0.391 + 0.011GA

0.0728

0.380

< 0.001

0.0097–0.0124 for GA

TV-E/A

–

0.422 + 0.011GA

0.0666

0.426

< 0.001

0.0099–0.0124 for GA

oICT

–

44.82–1.138GA + 0.0247GA2

5.51

0.038

< 0.001

− 2.292 – 0.0166 for GA

0.0031–0.0463 for GA2

oIRT

log10

1.491 + 0.0049GA

0.0607

0.147

< 0.001

0.0038–0.006 for GA

oLV-MPI

log10

−0.2757 - 0.0098GA + 0.0003GA2

0.0512

0.122

< 0.001

− 0.0206 – 0.0009 for GA

0.00005–0.00045 for GA2

pICT

log10

1.468–0.0026GA + 0.0001GA2

0.0812

0.063

< 0.001

− 0.0196 – 0.0144 for GA

− 0.0002 - 0.0004 for GA2

pIRT

log10

1.453 + 0.0054GA

0.0596

0.181

< 0.001

0.0044–0.0065 for GA

pLV-MPI

log10

− 0.3855 - 0.0044GA + 0.0002GA2

0.0592

0.141

< 0.001

−0.0168 – 0.0008 for GA

− 0.00006 - 0.0004 for GA2

TI

–

156.4 + 6.161GA - 0.0972GA2

13.84

0.139

< 0.001

3.26–9.062 for GA

− 0.1514 - -0.043 for GA2

RV-MPI

–

0.1191 + 0.0188GA - 0.0003GA2

0.0742

0.107

< 0.001

0.0033–0.0343 for GA

− 0.0006 - 0.00003 for GA2

  1. CPR, cerebroplacental ratio; CI, confidence interval; DV-E, early diastolic filling time of ductus venosus (sec); DV-PIV, pulsatility index for vein of ductus venosus; DV-S/a, systolic/atrial wave ratio of ductus venosus; GA, gestational age (weeks); MCA-PI, pulsatility index of middle cerebral artery; MCA-PSV, peak systolic velocity of middle cerebral artery (cm/sec); MV-E/A, E/A ratio of flow across mitral valve; oICT, isovolumetric contraction time measured by placing the caliper at the beginning of valve clicks (sec); pICT, isovolumetric contraction time measured by placing the caliper at the peak of valve clicks (sec); oIRT, isovolumetric relaxation time measured by placing the caliper at the beginning of valve clicks (sec); pIRT, isovolumetric relaxation time measured by placing the caliper at the peak of valve clicks (sec); oLV-MPI, myocardial performance index of left ventricle measured by placing the caliper at the beginning of valve clicks; pLV-MPI, myocardial performance index of left ventricle measured by placing the caliper at the peak of valve clicks; PF,; time from pulmonary valve opening to pulmonary valve closure (sec); RV-MPI, myocardial performance index of right ventricle; TI, time from tricuspid valve closure to tricuspid valve opening (sec); TV-E/A, E/A ratio of flow across tricuspid valve; r2, coefficient of determination; SD, standard deviation; UA-PI, pulsatility index of umbilical artery