Select a vessel and GA to see typical PI/RI/PSV ranges and whether your value is below, within, or above the band.
What this tool shows
- A broad, gestation-specific reference band for the selected vessel (umbilical artery or middle cerebral artery) and Doppler measure (PI, RI, or PSV).
- An optional comparison of your entered value against that band with a simple note (below / within / above typical).
How the ranges are generated
- Weeks are grouped into short intervals (e.g., 18–22, 23–27) that reflect the usual downward trend of UA PI/RI with advancing gestation and the characteristic MCA profiles used in practice.
- For each interval, the tool presents a rounded “typical” low–high band derived from commonly cited reference tables. PI and RI are unitless; PSV is shown in cm/s.
- Inputs are clamped to practical use (≈16–40 weeks). Outputs are rounded for readability (0–2 decimal places depending on measure).
Scope and limits
- Values are for quick orientation and counselling. Clinical interpretation depends on full ultrasound context (machine presets, sampling technique, fetal state) and local percentiles/MoM thresholds.
- Management commonly follows guideline frameworks for growth restriction and anemia surveillance (e.g., UA Doppler in FGR pathways; MCA-PSV for fetal anemia). Always use local protocols.
Sources
- ACOG Practice Bulletin: Fetal Growth Restriction (use of UA Doppler in surveillance). acog.org/.../fetal-growth-restriction
- ISUOG Practice Guidelines (updated): use of Doppler velocimetry in obstetrics (UA/MCA reference use and clinical application). openaccess.sgul.ac.uk/id/eprint/113549/
Last updated: 6 Oct 2025
How to use this calculator
- Choose the vessel (Umbilical artery or MCA) and Doppler measure (PI, RI, or PSV).
- Enter gestational age (weeks+days). Optional: add your measured value.
- Tap Lookup to see the typical band for that GA and how your value compares.
PI/RI are unitless; PSV is usually reported in cm/s.