Can anyone explain stonebirth to me?

Not sure I get it: so the corpse we crawl out of in MS1 is one that would have had the stonebirth ritual performed on them? So Vatra herself wouldn't have the ritual performed on her, but she would send essentially surrogate mothers into the world to have this c-section like procedure performed on them, thus extracting the foundlings? Are we one of the ones extracted through the stonebirth ritual or are we one of the seeds that Vatra sent directly to grow in the earth after lamenting the stonebirth ritual? It's the one aspect of the lore I just wrap my head around.