The length of the fetus from the crown (top of the head) to the bottom of the buttocks (the area above where legs begin) is called as Crown Rump Length (CRL). It is measured from 6 – 13 weeks of pregnancy. In this online CRL calculator, you can find the crown rump length for the number of weeks.
Typical CRL will be around 0.4cm for 6.1 Weeks, 1cm for 7.2 Weeks, and grow up to 8.0 cm at 14.0 weeks. The measurement is done using ultrasound scan.
Our crown-rump length calculator is the most accurate way to assess embryonic and fetal age and the duration of the early pregnancy.
Our tool will help you calculate the gestational age from CRL; we'll also talk about how accurate is an ultrasound in determining the age of the fetus at different stages of the pregnancy.
What is baby CRL and how to measure it?
CRL stands for the crown-rump length – the distance measured from the top of the head to the buttocks of an embryo (up to the 8th week after the conception date) or a fetus (8-14th week of the pregnancy).
Why do we use it?
To put it short: The CRL is used to determine the gestational age in the early stages of pregnancy. It's the most efficient way to find out your baby's age – the doctor should always compare it to the date of your LMP (last menstrual period).
When do we use it?
Perfect conditions for estimating your baby's age and use of the CRL charts are:
- Natural conception;
- CRL measurement between 9+0 and 13+6 weeks of pregnancy;
- Known last menstrual period;
- Regular menstrual cycles; and
- Without the use of the pill or breastfeeding during the previous 2 months.
Discovering the baby's age using CRL and ultrasound
So how exactly does it work?
Once your pregnancy test came out positive, your head was probably pounding with conflicting emotions and excitement; your next step should be a visit to your OB-GYN (obstetrics (pregnancy) and gynecology (female reproductive health) doctor) to confirm the age of the pregnancy (gestational age).
If your pregnancy is early on, your physician will:
- Ask you about the date of the first day of your last period;
- Perform an ultrasound examination, find the CRL and compare it to the crown-rump length chart; and
- Perform a full physical examination & take the detailed history.
If your pregnancy is more advanced, your physician will:
- Ask about your last period;
- Perform the ultrasound and check the length of your baby's head, bones, and belly – all these values will be then computed using the fetal weight percentile calculator; and
- Perform a full physical examination, e.g., check the fundal height & take the detailed history.
All this information is then computed, using special equations (usually built-in into the ultrasound machine), and compared against your last menstrual period date.
As a rule:
- I trimester (first trimester) measurements are used to determine the baby's age and the due date.
- II + III trimester measurements are used to assess the baby's growth, wellbeing, and rule out the possibility of any diseases or malformations.
How to use the crown-rump length calculator?
Our crown-rump length and gestational age calculator gives you a straightforward answer to your question – enter your CRL measurements into the proper field and await your result; in the format of hours, days, weeks, or mixed!
Our tool contains the functionality of a crown-rump length calculator in cm – you may choose any from 3 different units of the CRL.
Want to know more about the wonderful process of pregnancy? Let's take a tour from the beginning to the grand finale! Check our reliable tools from the Gynecology & Pregnancy category.
How to calculate gestational age with crown-rump length?
Here comes the time when we'd like to calculate gestational age from the CRL ourselves (or just replicate our CRL calculator's results); what's our first step?
Choosing the best equation possible. There are plenty of different formulas that we can use for assessing fetal age.
We decided to use the corrected Robinson and Fleming equation. The INTERGROWTH–21st Project, an international study of fetal growth, ranked it among the 4 most accurate fetal assessment equations.
On top of that, this equation is one of the easiest formulas found.
Gestational age (in days) = 8.052 × √(CRL × 1.037) + 23.73,
CRL is given in millimeters (mm).
A second option is to use a special CRL measurement chart; it's definitely easier than calculations but still more troublesome than using our crown-rump length calculator.
The crown-rump length chart:
|CRL (in mm)||Gestational age (weeks+days)|
|5||6 + 0|
|10||7 + 1|
|15||7 + 6|
|20||8 + 4|
|25||9 + 2|
|30||9 + 6|
|35||10 + 2|
|40||10 + 6|
|45||11 + 2|
|50||11 + 5|
|55||12 + 1|
|60||12 + 3|
|65||12 + 6|
|70||13 + 1|
|75||13 + 4|
|80||13 + 6|
|85||14 + 1|