Crown Rump Length (CRL) is the length of foetus from it’s top to bottom measured during a ultrasound scan. It’s the most accurate measurement of the gestational age of the foetus (baby). It will increase week by week in your pregnancy.
Measurement of Crown Rump length is usually done in your ultrasound scans and it’s a positive confirmation of your pregnancy . It increases from week to week as denoted in the below table
| Weeks from LMP | CRL (Crown Rump Length) in mm |
|---|---|
| 6 weeks Pregnant | 4-5 |
| 7 Weeks Pregnant | 9-11 |
| 8 weeks Pregnant | 15-20 |
| 9 weeks Pregnant | 20-29 |
| 10 weeks Pregnant | 30-41 |
| 11 weeks Pregnant | 42-54 |
| 12 weeks Pregnant | 55-69 |
| 13 weeks Pregnant | 70-84 |
| 14 weeks Pregnant | 85-100 |
Though the above values are approximate, this may differ in each pregnancy as these values also depend upon various factors such as quality of ultrasound scans, ability of the sonographer to take accurate measurements and also the fertilization age which is different from the gestational age..
According to some recent research, even some small errors in measurement of crown rump length might significantly affect the estimated fetal weight (A measurement error of -2 or +2 mm might cause the estimated fetal weight to be affected badly). And this may also lead to incorrect clinical assessment or diagnosis like baby behind a certain percentile according to gestational age so it’s very important to measure the correct CRL (Crown Rump Length)
Quality of the Ultrasound image also affects the measurement of CRL and it has been proven from research that the CRL varies from 5mm to -5mm when measured in different positions such as extension and flexion
The below table will show the crown lump data from Intergrowth 21st project where the data is collected by researchers from 18 different countries (In the table if its 7w+5d , it means 7 weeks 5 days and 3rd,10th,50th,90th and 97th refers to percentiles).. If it’s 10th percentile means, nearly 90% of the fetuses have a CRL which is greater than yours!
| CRL(mm) | 3rd | 10th | 50th | 90th | 97th |
|---|---|---|---|---|---|
| 15 | 7w+5d | 7w+6d | 8w+3d | 8w+6d | 9w+1d |
| 16 | 7w+5d | 8w+0d | 8w+3d | 9w+0d | 9w+1d |
| 17 | 7w+6d | 8w+1d | 8w+4d | 9w+1d | 9w+2d |
| 18 | 8w+0d | 8w+1d | 8w+5d | 9w+1d | 9w+3d |
| 19 | 8w+0d | 8w+2d | 8w+6d | 9w+2d | 9w+4d |
| 20 | 8w+1d | 8w+3d | 8w+6d | 9w+3d | 9w+4d |
| 21 | 8w+2d | 8w+3d | 9w+0d | 9w+4d | 9w+5d |
| 22 | 8w+2d | 8w+4d | 9w+1d | 9w+4d | 9w+6d |
| 23 | 8w+3d | 8w+5d | 9w+1d | 9w+5d | 10w+0d |
| 24 | 8w+4d | 8w+5d | 9w+2d | 9w+6d | 10w+0d |
| 25 | 8w+4d | 8w+6d | 9w+3d | 9w+6d | 10w+1d |
| 26 | 8w+5d | 9w+0d | 9w+3d | 10w+0d | 10w+2d |
| 27 | 8w+6d | 9w+0d | 9w+4d | 10w+1d | 10w+3d |
| 28 | 8w+6d | 9w+1d | 9w+5d | 10w+1d | 10w+3d |
| 29 | 9w+0d | 9w+2d | 9w+5d | 10w+2d | 10w+4d |
| 30 | 9w+0d | 9w+2d | 9w+6d | 10w+3d | 10w+5d |
| 31 | 9w+1d | 9w+3d | 10w+0d | 10w+3d | 10w+5d |
| 32 | 9w+2d | 9w+3d | 10w+0d | 10w+4d | 10w+6d |
| 33 | 9w+2d | 9w+4d | 10w+1d | 10w+5d | 11w+0d |
| 34 | 9w+3d | 9w+5d | 10w+2d | 10w+5d | 11w+0d |
| 35 | 9w+3d | 9w+5d | 10w+2d | 10w+6d | 11w+1d |
| 36 | 9w+4d | 9w+6d | 10w+3d | 11w+0d | 11w+2d |
| 37 | 9w+5d | 9w+6d | 10w+3d | 11w+0d | 11w+2d |
| 38 | 9w+5d | 10w+0d | 10w+4d | 11w+1d | 11w+3d |
| 39 | 9w+6d | 10w+1d | 10w+5d | 11w+2d | 11w+4d |
| 40 | 9w+6d | 10w+1d | 10w+5d | 11w+2d | 11w+4d |
| 41 | 10w+0d | 10w+2d | 10w+6d | 11w+3d | 11w+5d |
| 42 | 10w+0d | 10w+2d | 10w+6d | 11w+4d | 11w+5d |
| 43 | 10w+1d | 10w+3d | 11w+0d | 11w+4d | 11w+6d |
| 44 | 10w+1d | 10w+3d | 11w+1d | 11w+5d | 12w+0d |
| 45 | 10w+2d | 10w+4d | 11w+1d | 11w+5d | 12w+0d |
| 46 | 10w+3d | 10w+5d | 11w+2d | 11w+6d | 12w+1d |
| 47 | 10w+3d | 10w+5d | 11w+2d | 12w+0d | 12w+2d |
| 48 | 10w+4d | 10w+6d | 11w+3d | 12w+0d | 12w+2d |
| 49 | 10w+4d | 10w+6d | 11w+4d | 12w+1d | 12w+3d |
| 50 | 10w+5d | 11w+0d | 11w+4d | 12w+1d | 12w+3d |
| 51 | 10w+5d | 11w+0d | 11w+5d | 12w+2d | 12w+4d |
| 52 | 10w+6d | 11w+1d | 11w+5d | 12w+3d | 12w+5d |
| 53 | 10w+6d | 11w+1d | 11w+6d | 12w+3d | 12w+5d |
| 54 | 11w+0d | 11w+2d | 11w+6d | 12w+4d | 12w+6d |
| 55 | 11w+0d | 11w+3d | 12w+0d | 12w+4d | 12w+6d |
| 56 | 11w+1d | 11w+3d | 12w+1d | 12w+5d | 13w+0d |
| 57 | 11w+2d | 11w+4d | 12w+1d | 12w+6d | 13w+1d |
| 58 | 11w+2d | 11w+4d | 12w+2d | 12w+6d | 13w+1d |
| 59 | 11w+3d | 11w+5d | 12w+2d | 13w+0d | 13w+2d |
| 60 | 11w+3d | 11w+5d | 12w+3d | 13w+0d | 13w+2d |
| 61 | 11w+4d | 11w+6d | 12w+3d | 13w+1d | 13w+3d |
| 62 | 11w+4d | 11w+6d | 12w+4d | 13w+1d | 13w+4d |
| 63 | 11w+5d | 12w+0d | 12w+4d | 13w+2d | 13w+4d |
| 64 | 11w+5d | 12w+0d | 12w+5d | 13w+3d | 13w+5d |
| 65 | 11w+6d | 12w+1d | 12w+6d | 13w+3d | 13w+5d |
| 66 | 11w6d | 12w+1d | 12w+6d | 13w+4d | 13w+6d |
| 67 | 12w+0d | 12w+2d | 13w+0d | 13w+4d | 14w+0d |
| 68 | 12w+0d | 12w+2d | 13w+0d | 13w+5d | 14w+0d |
| 69 | 12w+1d | 12w+3d | 13w+1d | 13w+5d | 14w+1d |
| 70 | 12w+1d | 12w+3d | 13w+1d | 13w+6d | 14w+1d |
| 71 | 12w+2d | 12w+4d | 13w+2d | 14w+0d | 14w+2d |
| 72 | 12w+2d | 12w+4d | 13w+2d | 14w+0d | 14w+2d |
| 73 | 12w+3d | 12w+5d | 13w+3d | 14w+1d | 14w+3d |
| 74 | 12w+3d | 12w+5d | 13w+3d | 14w+1d | 14w+4d |
| 75 | 12w+4d | 12w+6d | 13w+4d | 14w+2d | 14w+4d |
| 76 | 12w+4d | 13w+0d | 13w+4d | 14w+2d | 14w+5d |
| 77 | 12w+5d | 13w+0d | 13w+5d | 14w+3d | 14w+5d |
| 78 | 12w+5d | 13w+1d | 13w+6d | 14w+4d | 14w+6d |
| 79 | 12w+6d | 13w+1d | 13w+6d | 14w+4d | 14w+6d |
| 80 | 12w+6d | 13w+2d | 14w+0d | 14w+5d | 15w+0d |
| 81 | 13w+0d | 13w+2d | 14w+0d | 14w+5d | 15w+1d |
| 82 | 13w+0d | 13w+3d | 14w+1d | 14w+6d | 15w+1d |
| 83 | 13w+1d | 13w+3d | 14w+1d | 14w+6d | 15w+2d |
| 84 | 13w+1d | 13w+4d | 14w+2d | 15w+0d | 15w+2d |
| 85 | 13w+2d | 13w+4d | 14w+2d | 15w+0d | 15w+3d |
| 86 | 13w+2d | 13w+5d | 14w+3d | 15w+1d | 15w+3d |
| 87 | 13w+3d | 13w+5d | 14w+3d | 15w+1d | 15w+4d |
| 88 | 13w+3d | 13w+6d | 14w+4d | 15w+2d | 15w+4d |
| 89 | 13w+4d | 13w+6d | 14w+4d | 15w+3d | 15w+5d |
| 90 | 13w+4d | 14w+0d | 14w+5d | 15w+3d | 15w+6d |
| 91 | 13w+5d | 14w+0d | 14w+5d | 15w+4d | 15w+6d |
| 92 | 13w+5d | 14w+1d | 14w+6d | 15w+4d | 16w+0d |
As you see the in the above table there can be difference of nearly 1 days to 2 weeks in crown rump length (CRL) growth accordingly to gestational age. In early pregnancy, foetus can be 3-7 days behind the growth which is completely normal but as the pregnancy progresses baby should not behind the growth by 2 weeks or more!