Crown-Rump Length of 4.8mm Corresponds to Approximately 6 Weeks Gestational Age
A CRL of 4.8mm corresponds to approximately 6 weeks + 0 to 6 weeks + 2 days of gestational age. 1, 2
Gestational Age Calculation
Using the INTERGROWTH-21st international standards, which represent the most robust methodology for CRL-to-gestational age conversion, a CRL of 4.8mm translates to approximately 42-44 days from the last menstrual period (6 weeks + 0-2 days). 1
- The INTERGROWTH-21st formula (GA = 40.9041 + (3.21585 × CRL^0.5) + (0.348956 × CRL)) provides the most accurate international standard for early pregnancy dating. 1
- This measurement falls within the early first trimester when CRL measurements are most reliable for pregnancy dating. 1
Clinical Context at This Gestational Age
At 6 weeks gestation with a CRL of 4.8mm, cardiac activity should be visible by transvaginal ultrasound if the embryo is viable. 3
- Cardiac activity is typically detectable by transvaginal ultrasound at approximately 6 weeks gestational age, with reliable visualization by 7 weeks in normal pregnancies. 3
- Any measurable embryo should demonstrate cardiac activity when using transvaginal ultrasound. 3
- Critical diagnostic threshold: If this embryo reaches ≥7mm CRL without cardiac activity, this definitively confirms embryonic demise. 4, 3
Important Caveats
The Robinson and Hadlock curves, while commonly used, show significant differences at this early gestational age compared to modern international standards. 5
- The Robinson curve underestimates gestational age by approximately 4 days at 6 weeks (difference of 3.7mm in CRL). 5
- At CRL measurements below 10mm, older formulas may underestimate gestational age by 1-9 days depending on the exact measurement. 2
- Use the INTERGROWTH-21st standards rather than older curves for the most accurate dating at this early gestational age. 1