I hate to break it to you, but the US Constitution does not protect the lives of even the post-born. Laws against murder, with rare exception, are state laws. As were the laws against abortion before Roe v. Wade.
It is unconstitutional for the any state to deprive one of life, without due process, meaning you are guilty of some crime. Is it OK for a state, city or individual to make their own law allowing infantacide? Or how about toddlercide? Didn’t think so.