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Gestational Age Formula:
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The CRL (Crown-Rump Length) to Weeks formula estimates gestational age in weeks from fetal crown-rump length measurement. This is a standard method used in early pregnancy ultrasound dating, typically between 6-13 weeks gestation.
The calculator uses the formula:
Where:
Explanation: This formula provides a reliable estimate of gestational age based on fetal size during the first trimester, when embryonic growth follows a relatively predictable pattern.
Details: Accurate gestational age determination is crucial for proper prenatal care, establishing expected due date, monitoring fetal development, and timing various prenatal tests and screenings.
Tips: Enter the crown-rump length measurement in millimeters (mm) as obtained from an ultrasound examination. The measurement should be from the top of the head (crown) to the bottom of the buttocks (rump).
Q1: How accurate is the CRL measurement for dating pregnancy?
A: CRL measurement is considered the most accurate method for dating early pregnancy, with an accuracy of ±5-7 days when measured between 6-13 weeks gestation.
Q2: Can this formula be used after the first trimester?
A: No, this formula is specifically designed for first trimester dating. After 13-14 weeks, other parameters (biparietal diameter, femur length) are used for dating.
Q3: What is the typical CRL measurement range?
A: CRL typically ranges from about 5-6 mm at 6 weeks to 70-80 mm at 13 weeks gestation.
Q4: Are there limitations to this calculation?
A: Accuracy decreases with poor measurement technique, certain fetal abnormalities, or multiple pregnancies. Always consult with a healthcare provider for clinical interpretation.
Q5: How does this compare to last menstrual period (LMP) dating?
A: Ultrasound dating using CRL is generally more accurate than LMP dating, especially when menstrual cycles are irregular or LMP date is uncertain.