Concerning patreon, they have this halfassed phrase in their tos that means anything and nothing. Especially since it contradicts itself.
"We also do not allow other fringe sexual fetish creations"
They cite incest as the first "example". Only, if one goes to a real adult site with real humans and sorts the content by US viewers, since patreon is US based, one will find that the top categories will include things like "step" and "family". They can think about this however they like, but claiming it is a fringe fetish is wishfull thinking.
Anyways, certain pregnancy content will be viewed by them as "other fringe", since they try to push their own views, for artificial pixels no less. To me, feet worshipping is fringe. But it is not offensive. So apart from whatever patreon uses as their makebelieve normal fetish range, I guess it depends how many "offended" people complain. So no showing the birth, might be enough to be safe. And no showing of x-ray penetration.
The situation is quite mind boggling for many things. Murder is illegal. Incest is illegal in most parts of the world and has a variable definition. It is possible to marry your cousin in many parts, yet you are still related by blood, and hence technically having incest. But then you add fiction and show a movie with murder in it. All is well. Then you show a movie, with actors and try to show incest and suddenly you are banned from the platform. And even the added layer of abstraction of not only using actors, but artificial pixels is not enough. I wonder if they ban text stories as well. Hmm. Seems not. I checked an adult site with a story section.
Sorry for ranting.