A Question for My Readers

A question that has recently puzzled me, because it has turned out to be harder to find an answer than one might think. It is often said that pro-lifers claim that an embryo or fetus is 'morally equivalent' to a child or adult. As I've noted before, this is not implied by the basic pro-life position -- which is just that the embryo or fetus has a basic right to life -- nor is it coherent in itself (since 'moral equivalence' in this context isn't a coherent notion -- the only sense that can be made of it is to understand it as 'having the same role in practical reasoning about moral matters' -- but no one holds that even adults are equivalent in this way, because our obligations even with regard to basic rights aren't the same toward everyone). But recently I started wondering which pro-lifers are making this claim. The claim seems, on the internet, at least, to be found only on pro-choice sites. The only use of moral equivalence I could find in a definitely pro-life context is in this testimony before the Senate, where it is said, "destroying or discarding an embryo in the laboratory is the moral equivalent of abortion," and this press release, where it is said, "It is also clear that few Americans believe a suction abortion to be the moral equivalent of a 'partial-birth abortion.'" Neither of these, however, are relevant to this point. So I'm wondering if there is some sort of pro-life source-text or source-texts at the root of it all that I've just not come across, or whether this is a case of summarizing the pro-life position without regard for what pro-lifers actually say. Does anybody have any insight on this?