🤰 Gestational Age from CRL (Ultrasound)
Date a first-trimester pregnancy from crown-rump length using the Robinson formula.
Clinical takeaway
First-trimester CRL is the most accurate dating method.
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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.
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Crown-rump length (CRL) | 45 mm |
|---|
→Estimated gestational age11w 2d
- Equivalent：79 days
- Formula：Robinson: GA (days) = 8.052·√(CRL·1.037) + 23.73
Frequently asked questions
- What is Gestational Age from CRL (Ultrasound)?
- Date a first-trimester pregnancy from crown-rump length using the Robinson formula.
- How is Gestational Age from CRL (Ultrasound) calculated? What is the core formula?
- GA (days) = 8.052 × √(CRL·1.037) + 23.73, with CRL in mm. Best at ~ CRL 15–95 mm (7–14 weeks).
- When is Gestational Age from CRL (Ultrasound) used?
- Estimate gestational age when CRL dating is most accurate.
- What are the key clinical points for Gestational Age from CRL (Ultrasound)?
- 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.
- What are the limits and cautions when using Gestational Age from CRL (Ultrasound)?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is Gestational Age from CRL (Ultrasound) calculated in practice? Can you show a worked example?
- Inputs: Crown-rump length (CRL) 45 mm → Result: Estimated gestational age 11w 2d（Equivalent: 79 days, Formula: Robinson: GA (days) = 8.052·√(CRL·1.037) + 23.73）