LUHE, that is not what the law says. It says that "any person ... who causes a child to die before it has an existence independent of its mother [which child at that point in time is capable of being born alive], shall be guilty of ... child
destruction [except if it is done in good faith to preserve
the life of the mother]".
There is no distinction between healthy or unhealthy children in the Infant Life (Preservation) Act of 1929.
There are only two exceptions. If the child is not capable of being born alive at the time of the abortion then an abortion is legal. Likewise, if it is necessary to save the life of the mother. However, any abortion of a living foetus performed after the twenty-fourth week of pregnancy but before the twenty-eighth week [i.e. before it is capable of being born alive] can only be done if the pregnancy would cause grave permanent injury to the woman, if the life of the woman is at risk, or if the child were born it would be seriously handicapped.
If a child is aborted after the twenty-seventh week that is the crime of child destruction. The only exceptions are if the woman's life is at risk due to the pregnancy, or if the child is not capable of being born alive.
If a child is intentionally killed once it is independent of its mother that is the crime of murder. There are no exceptions.
If a child is intentionally killed while a birth is in progress then the lawyers will have a field day deciding whether it is child destruction or murder, but my reading of the 1929 Act makes me think it would be child destruction.