In one of the Monty Python movies they have a skit about a woman who had agreed to be an organ donor and who is surprised one day when some men arrive at her home to take her liver. She’s not happy about it at all, but they throw her on the kitchen table and proceed to remove her liver while she protests and argues. It’s typical Python humor because it’s ridiculous.
Organ Donors sign paperwork indicating that they volunteer, under certain well-understood circumstances, to have their organs taken.
Babies in the womb haven’t filled out such paperwork.
Indeed, they never were provided the opportunity for it.