They could use a pretty basic utilitarian framework for that. Assume that if the mother dies, the child will die as well. On utilitarianism, a 55% chance of two people surviving is preferable to a 100% chance of one person surviving.
And this belief would probably turn off virtually every pro life women from the pro life ideology because pro lifers believe if she has a 45% chance of death from pregnency, then she should be forced to take that risk, making it harder to ban any abortions under any circumstances.
A society where 100% of the woman either were pro choice or become pro choice due to this argument means pro life dudes would have a much harder time spreading their genes and ideas, leading to society accepting legalized abortion until the moment of birth.
Pro life men would be like gay couples; unable to reproduce, and the onyl way they can spread their morals is through adoption with a woman that never becomes pregnant due to her not wanting to be forced to risk her life for a fetus (which this pro life dude would force her to take the risk), and society would come to the consensus that pro life is a subset of mysoginy because they want to force a woman to risk her life even if there is a 45% chance of death from pregnancy.
"Pro-life" is referring to the lives of diploid human organisms, not human cells. Maybe that's a vague label, but so is "pro-choice."
I do prefer the terms Pro Abortion Legalization (PAL) and ANti Abortion Legalization (ANAL); but the terms have yet to be adopted, so I code switch a lot.