The earliest time we can assess the babys sex is at 12 weeks gestation/pregnancy: We can tell the sex of the baby at the 12 week scan by assessing the direction of the nub. This is something that can be identified on babies at this stage and if it points vertically then it is likely to be a boy.

How accurate is gender ultrasound at 14 weeks?

Phenotypic gender confirmation was obtained from hospital records or direct telephone contact with women postnatally. Results: Results confirmed 100% accuracy in predictions made after 14 weeks gestation. The overall success rate in the first trimester group (11–14 weeks) was 75%.