Crown Rump Length (CRL) in Pregnancy

As soon as you begin your pregnancy journey, you come across a whole new set of terms and jargon that you were not familiar with before. From zygote and foetus to implantation and gestation- this 9-month-long pregnancy journey is about to enrich your vocabulary. One such term that you might be hearing often is CRL in pregnancy.

CRL is a common term used during ultrasounds in pregnancy. CRL fullform is crown rump length and it is done to estimate the gestational age of the growing foetus. CRL in ultrasound is usually done in the early days of pregnancy because the biological variability is very high at this time of the pregnancy.

In this article, we will learn more about CRL meaning in pregnancy, different measurements of CRL and its uses.

What is CRL in Pregnancy?

CRL in pregnancy is a measurement that denotes the length of the baby from the top of the head to the bottom of the buttocks. The limbs of the baby and yolk sac are not included in this measurement. CRL is done when the baby reaches six or seven weeks and can be done till the baby is of 14 weeks of age. The earlier the CRL in ultrasound is done, the more accurately it can tell the baby's measurement.

CRL Uses

Here are some of the uses of CRL in pregnancy:

1. Heartbeat detection

Once the crown rump length of the foetus exceeds 7mm, the doctor should be able to detect a heartbeat. If there is no heartbeat or cardiac activity, the pregnancy is likely a missed miscarriage. A missed or silent miscarriage can occur even without experiencing any of the normal miscarriage symptoms.

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2. Due date of the baby

CRL is a crucial ultrasound measurement used during pregnancy to determine gestational age and calculate the due date. The earlier the first ultrasound is performed, the more accurate the gestational age will be. In multiple pregnancies, CRL measurement of the fetuses is important for dating the pregnancies.

3. Gender of the baby

Additionally, when the CRL in ultrasound shows that the embryonic length has reached 76 mm or more, the chances of identifying the sex of the baby increase. The CRL measurement for boy and girl is the same at 6 weeks. This is because, in the early weeks of pregnancy, the cloacal folds that later become the penis or clitoris are in their development phase. It is in the CRL at 9 weeks that the gender of the baby can be determined more accurately.

4. Chromosomal anomaly identification

The importance of CRL in pregnancy also lies in the fact that a decrease in the crown rump length indicates some chromosomal anomalies, such as trisomy 18, also known as Edwards syndrome. Most of these complications are associated with the growth of the baby.

What is the Normal Crown Rump Length?

A normal CRL in pregnancy ensures that a child is growing and developing well. So, if someone is curious about the measurement of CRL at 7 weeks in cm of their child and wants to see if their baby has good growth, the following table of dating scan CRL can help them.

Here are some factors that can affect the CRL measurement:

• The age of the mother

• Habits of the mother, such as smoking

• The gender of the baby

• The presence of chromosomal disorders

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CRL Boy or Girl: What's the Connection?

There is a connection between crown-rump length (CRL) and determining the gender of a fetus during pregnancy. Male gender can already be reliably determined when CRL is 55 mm or more, which corresponds to a gestational age of 12 weeks or more. On the other hand, if CRL is less than 50 mm, which corresponds to a gestational age of less than 11 weeks and 4 days, gender determination may be more difficult. However, a difference in CRL does exist between male and female fetuses at 9-13 weeks of gestation, with male fetuses having a larger CRL compared to female fetuses.

But this is not a surefire way to determine the gender of a fetus. For parents wishing to know CRL measurement for boy or girl, it's better not to rely on it as CRL accuracy can be low during the earlier stages of pregnancy. We understand that the curiosity to know your baby's gender must be sky-high right now but it's better to wait and be surprised.

So, this was all one needs to know about crown rump length or CRL in pregnancy. By learning the CRL meaning in pregnancy, one can know whether their baby is growing well in the womb or not. But mostly, CRL helps doctors understand about the health, growth and development of the baby as well as the progress of the pregnancy.

References

1. Kang JY, Park EJ, Yang YS, Park M, Park WI. (2013). Crown-rump length measured in the early first trimester. NCBI

2. R Napolitano, J Dhami, EO Ohuma, C Ioannou, A Conde-Agudelo, SH Kennedy, J Villar, AT Papageorghiou. (2014). Pregnancy dating by fetal crown–rump length: a systematic review of charts. BJOG