Maybe you're right in Britain, but in the US there are no "certain circumstances" that make an abortion legally justifiable. Up to a certain stage of development, a mother can have an abortion just because she wants to. This suggests that the fetus has no rights whatsoever and is human tissue belonging to the mother, not a human being with limited rights.

Once the embryo is removed from the mother, though, this obviously changes. Now it is just as much part of the father as of the mother. So if the embryo does not have rights of its own, and it is not physically joined to the mother or the father so that their rights can extend to it, then whose rights does it have? It can actually survive just as well in someone else's womb, so your explanation of "can't survive without the mother" doesn't fit this case. So if it's not the parents' property then why can't another compatible woman walk in and claim it? I think the analogy of property rights is the best one we have. And whether it is property or not, why don't both parents have equal say about what happens to it?

What pdc said early on is right on target: nobody predicted this becoming an issue, so it is genuinely complex on all sides. It touches on medical rights, abortion rights, and, if you're correct, anti-slavery laws. To suggest that any outcome other than the mother having her way is barbaric, eg. "equivalent to a situation where a women was forced to have an abortion," is both simplistic and pointless. It's not equivalent to that, among other reasons because the mother will not be subject to a surgical procedure against her will. It is more equivalent, in my opinion, to a woman asking her boyfriend to impregnate her, him saying "okay," and then changing his mind later. It's good that he changed his mind BEFORE she was pregnant, I think. And if that was her last chance to have a child, she'll have to live without that experience; plenty of other women have had to because this kind of fertilisation was not possible until recently.