Crown-Rump Length In Pregnancy: How Is It Measured And What Are Its Uses

Crown-Rump Length In Pregnancy: How Is It Measured And What Are Its Uses

20 Jan 2023 | 5 min Read

Sudeshna Chakravarti

Author | 274 Articles

Throughout your pregnancy, your doctor may prescribe several different scans, tests, or procedures to ensure the proper growth and safety of your developing baby. Your ob-gyn usually recommends these tests based on your medical history, pregnancy-related complications, or genetics. One of the vital procedures that helps evaluate the growth and development of your baby is the CRL or crown-rump length measurement which helps measure your baby’s length in the uterus from top to bottom.

Read on, as we tell you more about CRL, what it tells about your baby, and how it is measured. 

What is Crown-Rump Length (CRL)?

What is Crown-Rump Length (CRL)?
This procedure helps your doctor track your baby’s heart rate and also check for chromosomal abnormalities / Image credit: Freepik

Crown-rump length or CRL is the measurement of the c-shaped embryo or the fetus from the top to bottom (crown to rump), excluding the limbs. In fact, this ultrasound scan is considered one of the most crucial measures for antenatal care during the first trimester and is usually performed between six and thirteen weeks of pregnancy. 

The crown-to-rump length, also known as the greatest length (GL), is an accurate measurement in centimetres that helps determine the age of your baby. It also helps to evaluate accurate gestational age, which helps your doctor know more about your baby’s health, and also estimate your date of delivery better.

What Does CRL Tell About Your Baby’s Health?

The crown-rump length scan will help your doctor learn about the early developmental stages of your baby. Some of the findings from this scan include:

  • Tracking your baby’s heart rate: The heart rate of an embryo between 6-6.2 weeks is around 100 beats per minute (bpm), which increases to 120-160 bpm between weeks 6.3-7. Your doctor will keep track of this through the CRL and gestational age to determine your baby’s health.
  • Monitoring fetal growth: Besides helping the development of your baby, the CRL also helps your doctor keep a track of your baby’s overall growth. This is why your doctor will keep on monitoring the length and mass of your baby throughout your pregnancy.
  • Identifying pregnancy complications: The scan also helps detect complications that may arise during the early stages of pregnancy. For instance, if MSD (mean gestational sac diameter) – CRL is less than 5 mm, then the risk of pregnancy loss is considered 8%. If the difference between MSD and CRL is between 6-10 mm, the risk is considered around 3-4%. However, if the difference is greater than 10 mm, the loss would be less than 1%. Identifying these symptoms in time will help you avoid any additional pregnancy complications.
  • Recognising abnormalities: Comparing the mean sac diameter and CRL also helps detect growth retardation in the fetus. Hence, taking this ultrasonographic screening during the first trimester is considered crucial as it helps your doctor figure out if your baby has any chromosomal abnormalities and risks, such as Down syndrome, Patau syndrome, and Edwards syndrome.

While a CRL is vital in the first trimester, it might not be an accurate measurement during the later stages of pregnancy, as your baby grows in size and becomes more active. This is why other obstetric scans are performed to monitor your baby’s development and aspects such as abdominal circumference, fetal length, and fetal biparietal diameter.

How Do Doctors Measure CRL?

How Do Doctors Measure CRL?
Avoid relying on CRL charts alone and consult your doctor for a more detailed evaluation / Image credit: Freepik

Doctors use various formulations to evaluate crown-rump length, gestational age, and other factors. One of them is a simple math equation that helps determine your gestational age using the CRL. According to that equation, the gestational age equals to six weeks plus CRL multiplied by a number of days [GA = 6 weeks + (CRL X Days)]. In addition to this, the doctors also use the crown-rump length chart as a reference for their primary evaluation. 

However, you should not always rely on charts determine CRL as they are only an approximation. Since every pregnancy is different, you may come across multiple dissimilarities while measuring CRL. Hence, it’s always better to consult your doctor and get regular reports regarding your baby’s health rather than relying on charts alone. 


The crown-rump length is a crucial procedure during pregnancy that enables doctors to measure the length of the fetus. The ultrasound scan is done during the early developmental stage, and allows doctors to assess complications, track fetal heart rate, and monitor fetal growth. Doctors also use CRL to evaluate your gestation age and expected due date. There are many ways to calculate CRL, including a crown-rump length chart and mathematical formulations, but it’s better to consult your doctor for any queries rather than relying on the chart.

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