no dark hair line down my belly yet??

Chelsie • My 1st born girl 🎀💗 My angel boy son 👼🏻💙 & My rainbow girl on the way due 5th oct 2017 🎀💗
I'm nearly 20 weeks and still haven't got that hair line down my belly Yet, I've just got a hairy belly but no distinctive line? Is this normal?