“Why would it be more strict by a goy?”
The same reason a goy is chayiv misa for theft.
“A Ben Noach who performs an abortion would be chayav misa whether it is murder or not, because misa applies to all Sheva mitzvos Bnei Noach. It’s also agreed, I believe, that where abortion is prohibited, only the person performing the abortion would be chayav. If the mother requested it but didn’t perform it, she would be chayav only for lifnei iver.”
Which means if it is a self-abortion, such as the over the counter or prescription medication she takes, the mother would be chayiv misa.