Maybe silly?

Mary • CP 12/20/17 MC 1/23/18 ALEYNA 11/18/18

This may be a silly question but... I’ve read and heard that the baby doesn’t really get anything from Mom until like week 9? Until the placenta forms embryo gets nutrition and whatever it needs from the yolk sac? So I’ve read about women continuing to smoke until then... but if that’s the case then why do we have to take prenatals in the very beginning? If supposedly the baby doesn’t receive anything from us until week 9/10 then it’s not absorbing the vitamins, no? I’ve attached information from Glow that I read a few days ago that says what I mentioned above. Is there truth to this?