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Gestational Age Formula:
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The CRL (Crown-Rump Length) based gestational age calculation estimates fetal age in weeks from the measurement of the embryo's length from crown to rump. This method provides an accurate assessment of gestational age during the first trimester of pregnancy.
The calculator uses the formula:
Where:
Explanation: The formula accounts for the linear relationship between fetal size and gestational age during early pregnancy, with 6 weeks being the baseline when CRL measurement becomes reliable.
Details: Accurate gestational age estimation is crucial for determining expected delivery date, monitoring fetal development, scheduling appropriate prenatal tests, and making informed decisions about pregnancy management.
Tips: Enter crown-rump length in millimeters (mm) as measured by ultrasound. The measurement should be taken during the first trimester (typically between 6-13 weeks) for optimal accuracy.
Q1: Why use CRL for gestational age estimation?
A: CRL provides the most accurate method for dating a pregnancy in the first trimester, with an accuracy of ±3-5 days.
Q2: What is the typical range for CRL measurements?
A: CRL is typically measurable from approximately 6 weeks gestation (CRL ~4mm) up to 13-14 weeks gestation (CRL ~80mm).
Q3: How should CRL be measured?
A: CRL should be measured in a neutral position with the fetus in a straight line from the top of the head (crown) to the bottom of the buttocks (rump), excluding limbs.
Q4: Are there limitations to this calculation?
A: Accuracy decreases after the first trimester as fetal growth becomes more variable. Other biometric measurements (BPD, HC, AC, FL) are used for dating in later pregnancy.
Q5: How does this relate to estimated due date (EDD)?
A: Estimated due date is typically calculated as 40 weeks from the first day of the last menstrual period, or can be derived from the gestational age calculation.