CRL in Pregnancy – What is It and Normal Measurement Chart

6 min read

Written by Ajanta Biswas

Ajanta Biswas

CRL In pregnancy

The emergence of two red lines in your pregnancy test kit confirms pregnancy. But that is not the end of testing. In fact, it is the beginning of a series of tests and ultrasounds that you will have to go through for the next nine months. All these are important and you need to conduct them within time. These timely tests reduce the chances of miscarriages, birth defects, and life-threatening problems such as Down syndrome or Edward syndrome. CRL in pregnancy is one such test that you will have to take during your first pregnancy ultrasound.

CRL or Crown Rump Length in pregnancy is an essential test that plays a vital part in measuring the growth of the fetus according to its gestational age. Your doctor will predict your expected delivery date on the basis of the first CRL. The first heartbeat of your baby is detected based on the CRL. CRL lets you know when the gender determination test of the baby will be reliable. So let us know in detail about CRL in pregnancy and its uses.

In This Article

What is CRL in Pregnancy?

CRL is a particular type of evaluation that your gynecologist will conduct during your first pregnancy ultrasound scan after conception. It helps them in measuring the gestational age and assessing the growth of your baby beginning from early pregnancy till the end of the first trimester (6-13 weeks). 

In CRL, the doctor will only measure the distance between the head or crown and the buttocks or rump of the fetus. The measurements of the limbs or the amniotic fluid-filled sac are excluded here. The measurements will be taken in centimeters and then the doctor will compare the growth of the fetus according to the standardized gestational growth chart to conclude if the fetus is growing at a normal rate or not. 

The earlier you conduct CRL the more accurate it will be in predicting gestational age. A journal on Maternal-Fetal & Neonatal Medicine shows that CRL tests taken in between 7 to 9 weeks have only a 3 to 5-day variation between actual gestational age and predicted one. But at 12 weeks CRL the variation will rise for over a week. 

[Read : First Ultrasound During Pregnancy]

Full Form of CRL in Pregnancy

Full Form Of CRL In Pregnancy

The full form of CRL is the Crown-Rump-Length test. This test will occur during your first transvaginal ultrasound scan. As the length from the crown or head to the rump or bottom of the fetus is taken in this test, it is named as Crown-Rump-Length test or CRL.

The Normal CRL Chart in mm

The CRL or Crown-Rump-Length will vary according to the gestational age of the fetus. There is a generalized gestational age chart made by Robinson in the year 1975 that doctors still usually follow as a reference. Here is the CRL measurement chart for your help;

Gestational Age (In Weeks) CRL(In mm)
6 weeks 4 mm
7 weeks 11 mm
8 weeks 17 mm
9 weeks 23 mm
10 weeks 34 mm
11 weeks 44 mm
12 weeks 57 mm
13 weeks 68 mm
14 weeks 81 mm

Your CRL report can slightly differ from the normal CRL chart which is completely fine. A lot of factors like the age of the mother, her smoking or drinking habits, stress, amount of folic acid in the body, etc can impact the CRL report. While slight variations are harmless, a significantly small or large CRL can indicate serious issues. Decreased CRL can indicate chromosomal disorders whereas a large CRL measurement can indicate either that the fetus is older than its predicted gestational age or is larger than its gestational age.    

Uses of a CRL in Pregnancy

Uses of CRL

There are multiple uses of CRL. Not only gestational age, but CRL can also detect a first heartbeat, fetal abnormalities, and a missed miscarriage. CRL also has a positive connection with the healthy birth weight of the baby. Here are the uses of CRL

1. Heartbeat Detection

The detection of a fetal heartbeat confirms a life inside you. The heartbeat of the fetus can be heard around 6 weeks or 34 days of pregnancy. CRL can successfully detect fetal heart rate. Your doctor can hear fetal heartbeat once the fetus’s CRL reaches 7 mm. 

If there is no heartbeat at this stage then it indicates a missed miscarriage. A missed miscarriage or a silent miscarriage is a condition where the body fails to recognize the death of the fetus and continues to produce pregnancy hormones. 

2. Due Date of the Baby

Due date is very important whether you are opting for a normal delivery or a cesarian c-section. The due date is the approximate date of delivery that the doctor predicts by calculating the gestational age of the baby by noting down the LMP or last menstrual period of the mother before conception. 

Labor pain generally occurs around the due date if the calculations fall correctly according to the actual time of conception. For this doctors normally rely on calculating gestational age. 

But for women with irregular periods, it becomes difficult to confirm the gestational age and thus the due date. CRL can help the doctor to conclude by simply comparing the results of the CRL with the standardized CRL chart. So there will be fewer chances of extremely early or delayed delivery in comparison to the expected due date. 

[Read : How To Calculate Pregnancy Weeks And Months?]

3. Chromosomal Anomaly Identification

The chromosomal anomaly can be detected through the Crown Rump Length test. If the CRL measures show a significantly low measurement than the normal growth rate according to the gestational age then it indicates chromosomal abnormalities. 

Chromosomal abnormalities can lead to many problems such as Down syndrome, Edward syndrome, Patau syndrome, etc. Timely detection of such chromosomal anomalies can help the doctor to take necessary actions. Early detection of such abnormalities also helps you decide whether you want to go ahead with the pregnancy or not. 

Connection Between CRL and Gender Prediction

Connection Between CRL And Gender Prediction

There is a connection between CRL and the detection of the gender of your baby as we have discussed already. But if you are expecting the gender prediction based on CRL, then it is not possible. 

You will have your first CRL in 6 or 7 weeks of pregnancy. This is the first-trimester CRL that is done mainly to confirm a live pregnancy without abnormalities and to predict the gestational age. For the detection of the gender of your baby, you will have to go through another CRL in your second trimester. 

This is because the development of the genitals starts after 9 weeks. And you can see visible differences in the genitals of boys and girls after 12 weeks of gestation. A report published in Obstetrics & Gynaecology claims that the CRL of a male fetus measures slightly from a female fetus of the same gestational age. But there is no concrete evidence to support this view. So you have to wait patiently until your second trimester to know whether you are having a prince or a princess at your home. 

So CRL is one of the primary and trusted methods of calculating the age of the growing fetus inside you. Sometimes, inaccuracies or a margin of variations of 5 to 10 mm can occur in CRL. It can lead to errors in the calculation of gestational age and due date. If by any chance, anything seems wrong in your first CRL, then the doctors may redo the test before driving any conclusion. Also, try to take the first CRL as soon as possible or between 6 to 13 weeks. After that, CRL will not be an accurate method to decipher gestational age. 


1. How is CRL Calculated?

There are various formulas to calculate CRL, gestational age, and weight of the baby. The simple formula for calculating gestational age with the help of CRL is [Gestational Age= 6 weeks + (CRL * days)]. So the gestational age is calculated by multiplying the CRL measurement by the number of days and then adding it to 6 weeks. 

2. What Week is the Baby’s Gender Developed?

It is around 9 weeks of pregnancy when the development of the genitals of the fetus starts. And it is around 12 weeks when a visible difference can be seen between a male and female fetus’s genitals during the ultrasound test. Male gender can be detected with a minimum 55 mm  CRL. Whereas to confirm the female gender it is best to wait until a CRL of 60 mm. 

Read Also: All About Nuchal Translucency Scan

Ajanta Biswas,MA (English)

Studying English literature has been highly instrumental in creating a love for English and World Literature for this writer. Ajanta has been writing for more than two years. She specializes in creating short and crisp blogs that can create awareness among women about healthy pregnancy and among parents about better parenting.Read more.

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