Umbilical Artery Doppler reference values (3rd trimester)
In low-risk singleton pregnancies, reference centile values for umbilical artery (UA) pulsatility index (PI) and systolic/diastolic ratio (S/D ratio) decrease with advancing gestational age using the INTERGROWTH-21st standardized protocol. [1]
Pulsatility index (PI) normal values by gestational age
These values are UA-PI centiles for GA 30–40 weeks. [1]
- 30+0 weeks: 50th 1.00, 95th 1.28
- 32+0 weeks: 50th 0.63, 95th 0.73
- 34+0 weeks: 50th 0.92, 95th 1.19
- 36+0 weeks: 50th 0.88, 95th 1.14
- 38+0 weeks: 50th 0.84, 95th 1.08
- 40+0 weeks: 50th 0.79, 95th 1.03
Systolic/Diastolic (S/D) ratio normal values by gestational age
These values are UA S/D ratio centiles for GA 30–40 weeks. [1]
- 30+0 weeks: 50th 2.81, 95th 3.89
- 32+0 weeks: 50th 2.68, 95th 3.67
- 34+0 weeks: 50th 2.56, 95th 3.46
- 36+0 weeks: 50th 2.44, 95th 3.24
- 38+0 weeks: 50th 2.32, 95th 3.03
- 40+0 weeks: 50th 2.19, 95th 2.81
Clinical use of “normal” vs “abnormal” values
“Normal” UA Doppler interpretation is typically based on centiles (commonly the upper 95th centile for PI or S/D ratio) using a matching reference chart and standardized measurement technique. [1]