Measuring Parameters & Reference Values – Doppler in NT Screening

Measuring Parameters & Reference Values – Doppler in NT Screening

---

1. Ductus Venosus (DV) Flow:

• Waveform: Triphasic – S, D, and a-wave
• Normal: Forward flow during a-wave
• Abnormal: Reversed or absent a-wave
• Reference: Normal in 98–99% of euploid fetuses

2. Tricuspid Valve Regurgitation (TR):

• Measurement: Color Doppler + Pulsed Doppler across tricuspid valve
• Normal: No regurgitation or brief regurgitation < 60 cm/s
• Abnormal: Regurgitant jet > 60 cm/s, duration > 50% of systole
• Reference: TR is abnormal in ~50% of trisomy 21 cases

3. Uterine Artery Doppler (UtA):

• Measurement: Pulsatility Index (PI)
• Normal: Mean PI < 1.4 (at 11–14 weeks)
• Abnormal: High PI > 95th percentile (↑ risk for preeclampsia)

4. Umbilical Artery Doppler (optional in early scans):

• Normal: Low resistance, forward flow in diastole
• Abnormal: High resistance or absent/reversed end-diastolic flow
• Note: Primarily assessed in second trimester or if severe growth restriction suspected early

5. Crown-Rump Length (CRL):

• Measurement Range for Doppler: 45–84 mm (11–13+6 weeks gestation)
• Reference: Ensures NT and Doppler markers are evaluated within standard FMF criteria