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The Crown-Rump Length (CRL)

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This module details the Crown-Rump Length (CRL) measurement, the gold standard for first-trimester dating. It provides step-by-step guidance on identifying the longest fetal axis and maintaining the precise orientation required for a reliable assessment.

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1. Using a transvaginal transducer, what is the minimum CRL at which an embryo can be reliably identified?
1 mm 2 mm 5 mm 10 mm
2. When the Mean Sac Diameter (MSD) reaches ~14 mm, what CRL is the embryo expected to have?
2 mm 5 mm 8 mm 12 mm
3. Which measurement provides more accurate gestational age estimation in early pregnancy?
Mean Sac Diameter (MSD) Crown-Rump Length (CRL) Both are equally accurate Biparietal Diameter (BPD)
4. To ensure the most accurate CRL measurement, how many good images should be averaged?
1 2 3 5
5. What is the ideal gestational window for CRL-based dating to achieve the highest accuracy?
4–5 weeks 6–9 weeks 10–12 weeks 13–15 weeks
6. Once gestational age has been established by an early CRL or MSD measurement, what should you do if a later scan suggests a different age?
Always update GA to match the latest scan Average the two estimates Keep the original GA — do not revise it Recalculate GA using BPD instead
7. What does Crown-Rump Length (CRL) measure in early pregnancy?
The length from the top of the fetal head to the fetal legs The length from the top of the fetal head (crown) to the bottom of the torso (rump) The length of the fetus from the crown to the feet The circumference of the fetal head
8. Crown-Rump Length (CRL) is the most reliable method for dating pregnancies between 6 to 14 weeks of gestation.
True False
9. Which of the following is the ideal time frame for obtaining an accurate Crown-Rump Length (CRL) measurement?
5-6 weeks of gestation 6-9 weeks of gestation 9-12 weeks of gestation 11-13 weeks of gestation
10. The Crown-Rump Length (CRL) measurement can be used to estimate gestational age up to 14 weeks of pregnancy.
True False
11. How does CRL contribute to screening for chromosomal abnormalities in the first trimester?
It is combined with nuchal translucency (NT) and biochemical markers to assess risk for Down syndrome It provides definitive diagnosis for Down syndrome It is used to rule out all fetal abnormalities It is used alone to assess fetal risk for genetic disorders
12. While CRL is highly accurate, limitations include challenges in measurement when the fetus is in an abnormal position or in cases of maternal obesity.
True False