I don't see why a mum-to-be can't join, i suppose its a way of seeing what you can get up to once the little one is there, and a way to meet people! Perhaps unusual though... The 30CHFs sign up fee is for one calender year, so it doesn't matter if you sign up now or after the birth...
I know the
LLL encourage mums-to-be to come along to their meetings - if you're planning on breastfeeding at all, then maybe you could try the english speaking in group in Zurich - link
here. Maybe a good way to multitask - meet some mums/mums-to-be and also make good contacts for english-speaking bfeeding support.
Good luck for April!