[TOMT][Book] In a near-apocalyptic scenario, a set of historical reenactors contribute to saving society

Sorry, this is very vague, but I remember a book where a woman is in an ultra-modern city but finds that it is crumbling. She thinks (or is told) to run (through the jungle? woods?) to a town where wealthy people have been, for fun, recreating a medieval society.

The most specific detail I remember beyond that is that she was mortified to learn that she would have to have a baby the "old fashioned" way, without an external incubation pod.