Gestational Age from Crown–Rump Length Calculator

Overview

Estimates gestational age from first-trimester crown–rump length using the Robinson–Fleming relationship.

Clinical Significance

CRL is most accurate within the validated first-trimester range and should be measured using standard ultrasound technique.

When to Use

• Use when the calculation is relevant to the clinical question.
• Confirm that the population and units match the validated method.
• Use current and reliable measurements.

How It Is Calculated

• Gestational age in days ≈ 8.052 × √CRL(mm) + 23.73.

Interpretation

• CRL is most accurate within the validated first-trimester range and should be measured using standard ultrasound technique.
• Interpret alongside the full clinical picture and current guidance.

Worked Example

Enter the required measurements in the stated units. MedicalC then applies: Gestational age in days ≈ 8.052 × √CRL(mm) + 23.73.

Patient Considerations

• Consider age, body size, pregnancy, organ function and treatment effects where relevant.
• Repeat the calculation when inputs or clinical status materially change.

Limitations

• Accuracy depends on the quality and units of the entered data.
• The equation may not be validated in every patient population.
• This tool does not replace clinical judgement or specialist advice.

Clinical Pearls

• Check units before calculating.
• Document the source and timing of each input.
• Use trends where clinically appropriate.

Common Mistakes

• Mixing SI and conventional units.
• Using non-contemporaneous measurements.
• Treating the output as a diagnosis or prescription.

Evidence Base

The implemented calculation follows the published or guideline-based relationship: Gestational age in days ≈ 8.052 × √CRL(mm) + 23.73.

References

1. Robinson HP, Fleming JEE. A critical evaluation of sonar crown-rump length measurements. Br J Obstet Gynaecol. 1975. — Primary publication, guideline or established source supporting the calculation.