Hey A, I hope you're still reading my blog (and that you had great beta doubling numbers!). My yoga teacher gave me two people to contact in Paris for yoga classes. She told me she's not sure they're doing specific prenatal yoga classes, but if not, they should be able to direct you to someone who does.
1: Sylviane Gianina
sylvianegianina [at] gmail [dot] com
2: Marina Margherita
marina [dot] margherita [at] orange [dot] fr
Hope this helps!