Pulsed-wave Doppler peak velocities (m/s) and E/A ratios, Z-scored by gestational age (Gagnon 2016, validated 18–39 weeks). Fetal inflow is A-wave dominant (E/A < 1); E/A rises gradually with gestation as ventricular compliance improves — elevation is a sign of ventricular dysfunction in FGR and TTTS.
Isthmus systolic VTI (m), diastolic antegrade VTI (m), and isthmic flow index (IFI = (systolic+diastolic)/systolic). Negative or absent diastolic flow indicates elevated right-sided afterload — a key finding in FGR.
Enter RV end-diastolic area (EDA) and end-systolic area (ESA) from the 4-chamber view. FAC = (EDA − ESA) / EDA × 100. Z-scored by gestational age (Luewan 2011) and by estimated fetal weight (Messing 2011). FAC < 30–35% in the context of FGR or TTTS suggests significant systolic dysfunction.
Measure filling time (valve opening to closure, diastole) and ejection time from PW Doppler; cycle length = RR interval (ms). FTF = filling/cycle × 100, ETF = ejection/cycle × 100. Shortened filling fraction is an early sign of diastolic dysfunction in FGR. Reference: Carvalho 2017 (filling), Carvalho 2002 (ejection).
SV = π/4 × D² × VTI (cm³); CO = SV × HR (mL/min). Combined cardiac output is indexed to estimated fetal weight. Reference range for indexed combined CO: 425–550 mL/min/kg (Mielke 2001). Increased CO is seen in fetal anaemia and early FGR compensation; decreased CO reflects late decompensation.
Non-GA-dependent fixed reference (Tulzer 1991): mean 2.46, normal range 1.94–2.98 (mean ± 2SD). Low PI (ductal constriction) occurs with maternal NSAIDs; high PI occurs with tocolytics (terbutaline) or duct-dependent systemic circulation (e.g. HLHS). This index deliberately does not enter the Z-score findings.