Regular check-ups, pre-natal 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
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 the 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.
The CRL scan assists your doctor in evaluating the well-being and development of your baby in the womb. An average baby measures is 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:
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.