Baby measuring ahead.

Zoe • Pregnant with second baby! Momma if one baby boy! 💙💙💙💙💙💙💙💙💙💙💙💙💙💙💙💙

So I was supposed to be 8w2d and my ultrasound said I’m exactly 9w today. I only had sex once the month of December so I am confused why my date is off?.