🤰 Gestational Age from CRL (Ultrasound)
Date a first-trimester pregnancy from crown-rump length using the Robinson formula.
Gestational Age from CRL (Ultrasound)
Crown-rump length (CRL) (mm)
When to use
Estimate gestational age when CRL dating is most accurate.
How it works
GA (days) = 8.052 × √(CRL·1.037) + 23.73, with CRL in mm. Best at ~ CRL 15–95 mm (7–14 weeks).
Key points
- First-trimester CRL is the most accurate dating method.
- Does not apply at very small or large CRL.
- Use BPD/HC/AC/FL for later pregnancy.
References
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.