Aortic isthmus Doppler velocimetry:
AoI Doppler was assessed in the cross-sectional 3VT view.
The 3VT view was obtained at the level of the fetal mediastinum by moving the transducer obliquely cephalad from the four-chamber view. At this point, the pulmonary trunk, ductus arteriosus, aortic arch, AoI and superior vena cava are clearly demonstrated, with the aortic and ductal arches forming a V configuration pointing to the posterior spine. The V shape shows the convergence of the AoI and the arterial duct, helping to identify where the range gate should be placed. Once the vascular segment identified, colour-directed pulsed-wave Doppler was adjusted to high velocities so that the great vessel’s blood flow will be homogeneous in colour and will show no aliasing. The pulsed wave gate size was adjusted to avoid recording signals from the adjacent vessels. Velocity waveforms were recorded during fetal quiescence with the angle of insonation close to 0° and no more than 30°.
The aortic isthmus waveform was assessed as presence of diastolic flow or absent or reversed diastolic flow (Figure 1A and 1B). In cases of some reversal of diastolic flow but predominant antegrade flow, it was considered as antegrade flow while if predominant flow is retrograde then it was considered as retrograde flow in aortic isthmus. When there was no flow in the diastole was taken as absent diastolic flow in AoI.
Staging of IUGR- After growth assessment and doppler study, IUGR stage was assigned by using staging system given by Gratacos et al 2014[12]. The Doppler parameters and impedance indices were plotted against established centiles for gestation using Barcelona fetal medicine reference charts.
Statistical analysis was performed using SPSS 23.0 Doppler variables and perinatal outcome were analyzed by Pearson’s Chi-square or Fisher’s exact test as indicated. The predictive value of the AoI and other Doppler variables in predicting adverse perinatal outcome was assessed by estimation of sensitivity, specificity, predictive values and likelihood ratios and by multiple regression analysis.
Delivery of IUGR fetuses was decided depending upon weeks of gestation and doppler flows and by an abnormal fetal heart rate trace (Table 1). Retrograde flow in aortic isthmus was not used as a trigger for delivering these fetuses.Mode of delivery was by emergency Caesarean section in these cases, irrespective of the stage of IUGR as a routine protocol of the institute .Protocol for follow up and delivery was followed as mentioned in above staging system.