Crown Rump Length (CRL) on Ultrasounds

baby in the womb on ultrasound

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Crown-rump length (CRL) is an ultrasound measurement that is used during pregnancy. The baby is measured, in centimeters, from the top of their head (crown) to the bottom of their buttocks (rump). The limbs and yolk sac are not included in the measurement. The CRL can be measured starting around six or seven weeks of pregnancy up until 14 weeks.

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What Is Crown-Rump Length?

CRL may be useful in calculating gestational age. With this gestational age, doctors can estimate your potential due date. The earlier the first ultrasound is performed, the more accurate the baby's gestational age will be.

Once the fetus has developed past 14 weeks, head circumference, biparietal diameter, and femur length measurements are used to determine how the baby is progressing. The length of the umbilical cord is typically the same as the CRL throughout pregnancy. 

Uses

Once the fetus's CRL surpasses 7 mm, a heartbeat should be detected by ultrasound. If no heartbeat or cardiac activity is detected, then the pregnancy is likely a missed miscarriage.

A missed, or silent, miscarriage typically occurs without the normal miscarriage symptoms. The placenta may continue to supply hormones, which can mask the outward signs of a miscarriage. 

Women with a mean sac diameter (MSD) of less than 5 mm greater than the CRL are more likely to experience a first-trimester miscarriage –– even if the baby has a normal heart rate.

Decreased crown-rump length can also diagnose chromosomal anomalies like trisomy 18 (Edwards syndrome) and other trisomies associated with growth restriction.

 

5 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Broere-Brown ZA, Baan E, Schalekamp-timmermans S, Verburg BO, Jaddoe VW, Steegers EA. Sex-specific differences in fetal and infant growth patterns: a prospective population-based cohort study. Biol Sex Differ. 2016;7:65. doi:10.1186/s13293-016-0119-1

  3. Murugan VA, Murphy BO, Dupuis C, Goldstein A, Kim YH. Role of Ultrasound in the Evaluation of First-Trimester Pregnancies in the Acute SettingUltrasonography. 2020;39(2):178-189. doi: 10.14366/usg.19043

  4. Kapfhamer JD, Palaniappan S, Summers K, et al. Difference between mean gestational sac diameter and crown-rump length as a marker of first-trimester pregnancy loss after in vitro fertilization. Fertil Steril. 2018;109(1):130-136. doi:10.1016/j.fertnstert.2017.09.031

  5. Sagi-Dain L, Peleg A, Sagi S. First-Trimester Crown-Rump Length and Risk of Chromosomal Aberrations-a Systematic Review and Meta-AnalysisObstet Gynecol Surv. 2017;72(10):603-609. doi: 10.1097/OGX.0000000000000490

By Krissi Danielsson
Krissi Danielsson, MD is a doctor of family medicine and an advocate for those who have experienced miscarriage.