Crown rump length

Last revised by Andrew Murphy on 23 Mar 2023

Citation, DOI, disclosures and article data

Citation:

Gaillard F, O'Shea P, Willmore N, et al. Crown rump length. Reference article, Radiopaedia.org (Accessed on 08 Dec 2023) https://doi.org/10.53347/rID-1186

DOI:

https://doi.org/10.53347/rID-1186

Permalink:

https://radiopaedia.org/articles/1186

rID:

1186

Article created:

2 May 2008, Frank Gaillard ◈

Disclosures:

At the time the article was created Frank Gaillard had no recorded disclosures.

View Frank Gaillard's current disclosures

Last revised:

23 Mar 2023, Andrew Murphy ◉

Disclosures:

At the time the article was last revised Andrew Murphy had no financial relationships to ineligible companies to disclose.

View Andrew Murphy's current disclosures

Revisions:

16 times, by 11 contributors - see full revision history and disclosures

Systems:

Obstetrics

Tags:

obstetrics, abr certifying ultrasound

Synonyms:

CRL (intrauterine measurement)
Crown rump length (CRL)

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.

Measurement

CRL is measured as the largest dimension of embryo, excluding the yolk sac and extremities. It is used as a primary measure of gestational age between 6-13 weeks. After 13 weeks, head circumference, biparietal diameter, and femur length measurements become more useful measurements for assessing fetal growth.

Practical points

The earlier in pregnancy a scan is performed, the more accurate the age assignment from crown rump length ⁴. If the original CRL measurement was adequate, the measurement is considered the baseline for all subsequent age measurements.

Overall, the accuracy of sonographic dating in the first trimester is +/-5 days (95% confidence range).

Cardiac activity should be present in an embryo with a CRL ≥7 mm ³. On a transvaginal scan performed by an experienced operator, absence of cardiac activity in an embryo with CRL ≥7 mm is diagnostic of a failed early pregnancy (missed miscarriage).

It has been reported that patients in whom MSD (mean sac diameter) is less than 5 mm greater than crown rump length (i.e. MSD - CRL = <5 mm) are prone to first trimester miscarriage, despite a normal heart rate.

Chromosomal anomalies, particularly trisomy 18 and triploidy are markedly associated with growth restriction, i.e. decreased crown rump length.