We have an "unlimited sick leave policy" where I work (at a Kantonal Hospital).
I had a month sick leave between 16 and 20 weeks and then will work 50% until 34 weeks when I stop completely. I have been paid at 100% during all this time and it won't affect my maternity leave at all which I have been told starts 2 weeks before birth -I might need to clarify that as others have said it starts at birth. Also, when taking holidays during the time I was working 50%, the holidays are calculated at 50% too so for every day I want off, I have 1/2day holiday and 1/2 sick. So long as you have a Dr. certificate, you should be fine.

Also have a look here