1. What is Crown-Rump Length (CRL)?

Crown-Rump Length (CRL) is the measurement of the length of human embryos and fetuses from the top of the head (crown) to the bottom of the buttocks (rump). It's the most accurate method for dating pregnancies in the first trimester (up to 13 weeks 6 days).

2. How Does the Calculator Work?

The calculator uses the Robinson formula:

Where:

• \( CRL \) — Crown-Rump Length in millimeters (mm)
• The result is converted from days to weeks + days format

Explanation: The relationship between CRL and gestational age is non-linear, which is why the square root function is used in the calculation.

3. Importance of Gestational Age Calculation

Details: Accurate gestational age determination is crucial for proper prenatal care, assessing fetal growth, scheduling important tests, and determining the estimated due date.

4. Using the Calculator

Tips: Enter the CRL measurement in millimeters (mm) obtained from an ultrasound scan. The measurement should be taken when the fetus is in a neutral position.

5. Frequently Asked Questions (FAQ)

Q1: How accurate is CRL for dating a pregnancy?
A: CRL is most accurate in the first trimester (±5-7 days). Accuracy decreases in the second trimester.

Q2: What is the typical CRL measurement range?
A: CRL is typically measured between 5-84 mm (approximately 6-14 weeks gestation).

Q3: When should CRL be measured?
A: CRL is most accurate between 8-13 weeks gestation. After this, head circumference or femur length may be better indicators.

Q4: Are there different formulas for different populations?
A: The Robinson formula is widely used, but some institutions may use Hadlock or other formulas with slightly different coefficients.

Q5: What if my ultrasound report already includes gestational age?
A: The ultrasound machine typically calculates this automatically. This calculator is for educational purposes or to verify calculations.