Just to add-in some places (like the ETH, where I work), maternity benefits increase once you've been employed for two years from the federal minimum (which is 14 weeks of 80% pay) to 4 months of 100% pay. So, sometimes, it pays to wait.
Also, you are not required to tell your employer that you are pregant, according to Swiss Federal law (source: http://geneva.angloinfo.com/information/11/birth.asp )
But, obviously, you won't be able to hide it forever.
I have told my employer twice about my pregnancies, and both times I told him as soon as I was sure that the pregnancy was viable and going normally (about 16 weeks), AND when I had a plan for when to return after the pregnancy (in my case, I was able to share my maternity leave with my husband, so I started working part time after three months of leave with my first).
From this experience, I found that coming in with a plan that demonstrates readiness to balance work and family responsibilities makes the pregnancy conversation easy for both employer and employee, and is more important than when the conversation takes place.
I would caution against trying to get information from your potential colleagues, since you don't want to get a reputation for being another one of those women who just wants maternity pay (it's ugly gossip, but very common). After all, will a boss who sticks to the rules dissuade you from having a baby? On the other hand, if people mention family-friendliness without you asking (or if you ask an open-ended question, like "what sort of qualities would you describe this employer as having?", take it seriously-I needed to work flex hours for 4 months after my maternity leave because we did not have a full time kinderkrippe spot, and it was absolutely wonderful to be able to do so more informally, as my boss is very family-friendly.
Whoa-sorry for the preaching. That was long!