Up to and including 13 6/7 weeks of gestation, gestational age assessment based on measurement of the crown–rump length (CRL) has an accuracy of ±5–7 days 11 12 13 14. Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11 15 16 17 18.
Why is CRL most accurate?
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.
What is a normal crown rump length?
Measurement of the mean gestational sac diameter is the first parameter that can be used to determine gestational age. • The rate of growth of the normal gestation sac is 1.1 mm/day. • Measurement of the crown–rump length (CRL) between 6 and 12 weeks is the most accurate dating parameter.
What if my CRL is less than expected?
Conclusions. There appears to be an association between a smaller than expected early CRL and a higher likelihood of first trimester miscarriage in singleton pregnancies conceived by IVF/ICSI. This data can be useful in clinical practice to assist in the decision of a re-evaluation by early scan.
How can you tell if boy or girl on ultrasound?
We can tell the sex of the baby at the 12 week scan by assessing the direction of the nub. This is something that can be identified on babies at this stage and if it points vertically then it is likely to be a boy. If it points horizontally then it is likely to be a girl.