Measurement of the crown–rump length (CRL) between 6 and 12 weeks is the most accurate dating parameter. CRL measurements of gestational age are accurate to within 3–5 days.

Why CRL is more accurate in first trimester?

Crown rump length (CRL) is the length of the embryo or fetus from the top of its head to bottom of torso. It is the most accurate estimation of gestational age in early pregnancy, because there is little biological variability at that time.

How accurate is CRL at 6 weeks?

At 6 weeks gestation there was an observed difference in CRL of 3.7 mm, equivalent to an underestimation of 4 days by Robinson. From 11 to 14 weeks gestation there was an observed difference in CRL of 0.9–1 mm, equivalent to 1 day overestimation by Robinson.

How accurate is CRL at 12 weeks?

At CRL ≥ 60 mm (gestational age ≥ 12+2) the feasibility was 97.4% and accuracy 100.0% (100.0% in male gender vs 100.0% in female gender).

What is a normal CRL at 6 weeks?

Even at 6 weeks we sometimes struggle to see the baby and its heart beat even when things are going fine. At 6 weeks the baby measures approx. 4mm from head to bottom, this is called the crown – rump length or CRL and is the measurement we use to date your pregnancy in the first trimester.

What size should the CRL be at 12 weeks?

Figure 1GA (weeks)CRL (cm, mean ± SD) MalesFemales103.89 ± 0.563.85 ± 0.50114.82 ± 0.774.76 ± 0.67125.73 ± 0.905.57 ± 0.86136.56 ± 0.976.10 ± 1.351 more row•16 Jun 2004