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Regular check-ups, prenatal screening, and scans are essential during pregnancy. Tests used in dating the pregnancy, estimating gestational age, and looking for chromosomal abnormalities might be prescribed by your doctor so that your pregnancy can progress smoothly. Estimation of the crown-rump length (CRL) of the foetus is one such scan.
Also Read: Common Trimester Wise Tests During Pregnancy
What is CRL?
CRL is the length of the foetus, measured from the top of its head to its buttocks. This measurement is in centimetres and doesn’t take into consideration the limbs or the yolk sac. Since CRL can be taken from about 6 to 7 weeks of pregnancy with an upper limit of 14 weeks, it is useful in calculating the gestational age of the foetus. The low biological variability at this stage of pregnancy makes it the most accurate estimation of your baby’s gestational age.
Once the gestational age is evident from the CRL, your doctor can provide an estimated delivery date. The earlier this scan is conducted, the more accurate it is. Note that the gestational age is different from the fertilisation age. Gestational age is calculated from the first day of your last menstrual period, whereas fertilisation age is typically two weeks less than the gestational age.
What Does Crown Rump Length Indicate About Your Baby’s Health?
The CRL scan assists your doctor in evaluating the well-being and development of your baby in the womb. An average baby measures about 51 cm tall and weighs around 3.5 kg at the time of birth. With this scan, it’s possible to find out your baby’s length and weight at different stages of your pregnancy. These are some issues that CRL helps to reveal:
- Presence of a heartbeat – If the CRL measurement is 7 mm or more, a transvaginal ultrasound can detect the foetus’ heartbeat. This type of ultrasound is conducted through the vagina instead of from outside which is how most ultrasounds are done.
- Miscarriage – A CRL can reveal the absence of a heartbeat and, in turn, a missed miscarriage. In such cases, the expecting mom doesn’t suffer from the usual symptoms of miscarriage like pain or bleeding. Also known as a silent miscarriage, the placenta keeps on producing the pregnancy hormone, leading the woman to believe that she is still pregnant.
- If your mean sac diameter (MSD) is less than 5 mm greater than the CRL measurement, a first-trimester miscarriage may be impending. This can occur in spite of detecting a normal heartbeat in your baby.
- CRL measurements that are on the lower side may also be indicative of chromosomal abnormalities such as Edwards Syndrome (trisomy 18), triploidy, or other growth-related problems.
- According to a study, there is a direct correlation between CRL measured before the 10th gestational week and birth weight. This is a one-of-a-kind study as other studies focus on the correlation between both factors only after the 10th week of gestation. A total of 632 ultrasound scans were performed on pregnant women who didn’t have any complications. The results indicated that there is a positive association between CRL in the early first trimester and the birth weight of the foetus. This can help to predict low birth weight (LBW) and ensure parents-to-be are emotionally prepared for premature delivery and newborn care.
Crown Rump Length Chart
The CRL diagram was first presented by Robinson in 1975 and is, still, the primary reference for pregnancy dating as well as evaluation. Below, we provide a CRL chart for your reference.
|Gestational Age in Weeks||CRL (mm)||Mass|
|6 weeks||4 mm||< 1g|
|7 weeks||11 mm||< 1g|
|8 weeks||17 mm||1 g|
|9 weeks||23 mm||2 g|
|10 weeks||34 mm||4 g|
|11 weeks||44 mm||7 g|
|12 weeks||57 mm||14 g|
|13 weeks||68 mm||23 g|
|14 weeks||81 mm||43 g|
These are the approximate foetus measurements at different stages of pregnancy. Other factors such as the mother’s age, smoking habits, and the amount of folic acid consumed may influence these measurements.
Every baby is different and slight variations in growth and development are normal. Your doctor’s benchmark measurements may also differ from the CRL chart. After a CRL scan, make sure you have a chat with your gynaecologist about your baby’s progress and ask for a detailed report on the same.
Also Read: Giving Birth To a Baby With Down’s Syndrome