Abortion problem solved.

fetus < 20 weeks old is not sentient
fetus > or = 20 weeks old is sentient

The argument that "it's the woman's body - she can do what she likes" becomes incoherent once you have a new life growing inside.

That said, it must be the responsibility (and priviledge) of BOTH parents to decide what happens to the child. Problems would happen when they can't work it out between them.

My answer: make abortion a punishable crime for which both parents must suffer, but abort a foetus they can't agree on.