Ultrasound measurement of the embryo or fetus in the first trimester (up to and including 13 6/7 weeks of gestation) is the most accurate method to establish or confirm gestational age.

Can you have a bump at 9 weeks pregnant?

Although you might only be showing a bit of a baby bump by week 9 of pregnancy - or in some cases, no bump at all yet -, you can probably feel your lower belly getting firmer. This is your uterus, which is expanding to fit your growing baby and will soon become a larger baby bump.