CRL measurement, i.e. how the baby grows in the mother’s belly

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CRL, or parietal-seat length, determines the length of the fetus, which is measured from the top of the baby’s head to the buttocks. CRL is, next to the size of the gestational bubble or the corpus luteum, one of the parameters measured during the ultrasound examination during pregnancy. What does CRL stand for and how is fetal length calculated? How fast does the baby grow in the mother’s womb and what is it like in the following weeks of pregnancy?

What is CRL?

The test that is most often performed during pregnancy and that gives the future mother the most information about the developing baby is ultrasound. This test is performed regularly to keep the information about your baby’s development up-to-date. Thanks to the ultrasound examination, you can not only see what the baby looks like in the mother’s belly, but also the doctor can determine many parameters important at a given stage of pregnancy. One of these parameters is CRL. The CRL is a parietal-seated distance that helps the doctor assess the age of the fetus and also diagnose whether the fetus is developing properly. The parameters that can be measured when performing an ultrasound examination are the size of the gestational sac, the size of the corpus luteum, the length of the child’s body, the circumference of the head, the bipolar dimension, the occipital-frontal dimension, the length of the femur and humerus, and the circumference of the abdomen.

CRL abbreviation expansion

The CRL abbreviation comes from the English term crown rump length, which in Poland is referred to as the parietal-seat distance. In an ultrasound scan, CRL is the distance measured between the top of a child’s head and the buttocks. This measurement does not include the legs, because the fetus in the uterus is in the embryonic position, i.e. tightly curled. It is therefore impossible to measure the length of the fetus from head to toe, and certainly not in the first trimester of pregnancy. CRL is one of the most important parameters measured during an ultrasound examination. On its basis, the exact age of pregnancy can be determined.

Calculation of the CRL of the fetus

Calculation of the fetal CRL is not one of the most complicated procedures. The doctor performing the examination draws a straight line from the top of the head to the buttocks of the fetus with the greatest possible precision on the obtained image. The measurement obtained in this way is referred to as the parietal-gluteal distance. CRL is measured during the first ultrasound examination of pregnancy. It is best for your baby if the first visit and the first examination will take place before the 10th week of pregnancy. The measurement calculated on this date allows the doctor to indicate the most reliable date of delivery. The CRL parameter is also very important in the diagnosis of fetal malformations. It is worth noting that other measurements also depend on the CRL measurement, including the measurement of the nuchal translucency, i.e. NT. This is due to the fact that a reliable NT measurement can only be performed when the fetal CRL is within 45-84 mm.

CRL during pregnancy – dimensions week by week

The CRL measurement result depends on the age of pregnancy and its standards are as follows:

  1. CRL at 5 weeks of gestation: 2 mm
  2. CRL at 6 weeks of gestation: 4 mm
  3. CRL at the 7th week of pregnancy: 7-13 mm
  4. CRL at the 8th week of pregnancy: 14-20 mm
  5. CRL at the 9th week of pregnancy: 20-30 mm
  6. CRL at the 10th week of pregnancy: 31-42 mm
  7. CRL at the 11th week of pregnancy: ~ 50 mm
  8. CRL at the 12th week of pregnancy: ~ 60 mm
  9. CRL at the 13th week of pregnancy: 65-78 mm
  10. CRL at the 14th week of pregnancy: 80-105 mm
  11. CRL at the 15th week of pregnancy: 100-115 mm
  12. CRL at the 16th week of pregnancy: 115-120 mm
  13. CRL at the 17th week of pregnancy: 120-130 mm
  14. CRL at the 18th week of pregnancy: 130-140 mm
  15. CRL at the 19th week of pregnancy: ~ 140 mm
  16. CRL at the 20th week of pregnancy: 140-150 mm

Later in pregnancy, the CRL measurement is replaced by the CHL measurement, in which the baby is measured from the top of the head to the heels.

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