Hi and welcome to the site.
For the entire first 7 days after conception, there is ZERO connection of the mothers blood with the babies. So no chance that anything she took by way of drugs or substances will pass to the baby during that time. During the next 7 days after that, the embryo is just starting to implant into the wall of the uterus
. SO only during this time slowly is there a connection to the mothers blood stream. So it isn;t until 14 days after conception that there is a meaningful connection between the mothers blood stream and the baby.
I hope this is reassuring.