Up to and including 13 6/7 weeks of gestation, gestational age assessment based on measurement of the crown–rump length (CRL) has an accuracy of ±5–7 days 11 12 13 14. Measurements of the CRL are more accurate the earlier in the first trimester that ultrasonography is performed 11 15 16 17 18.

Can CRL measurement be wrong?

Measurement of CRL is the method of choice for ultrasound assessment of gestational age in the first trimester,8 but it is susceptible to intra-observer and inter-observer variation. This may result from inconsistent or incorrect acquisition of the appropriate images.

Can we know gender by CRL?

Conclusions: Fetal gender may reliably be determined when CRL ≥ 60 mm (gestational age ≥ 12+2). Male gender may already be reliably determined when CRL ≥ 55 mm (gestational age ≥ 12+0). If CRL < 50 mm (gestational age < 11+4) the gender cannot be reliably predicted.

What should a baby measure at 8 weeks?

At 8 weeks baby now measures 16mm in length and has a clear head and body. If you are lucky you can sometimes see the small arm and leg buds developing.