With DS1 I just didn't tell people for a while. Like 30 weeks. We were living overseas and we told local friends (we only had a few) around 16 weeks. But everyone back home? We never posted a Facebook announcement and we didn't talk to most of our friends because of the huge time difference. I think my sister made a big deal of me "liking" BumGenius's FB page around 30 weeks and some people caught on then.
We told our parents and siblings around 14 weeks.
We had just gotten married and I didn't want people obsessively doing math to figure out if I got pregnant before we got married. The whole idea of that squicked me out. Plus, my husband had a meeting with some members of a foreign government when I was about 7 weeks, and they asked him how the baby was. We hadn't told anyone and I hadn't even been to the doctor yet. That really, really, really creeped me out. After that I just didn't want to discuss it with anyone.
Huh? How did they know?
We were told when we moved in that we we're almost certainly under audio surveillance and maybe video, because of H's position. Security swept our house once a month, but either it wasn't enough or they missed something.
msniq tried to hide it all the way until the anatomy u/s, but on a trip with her brother, she didn't drink beer and avoided soft cheese & deli meats and he figured it out. He didn't tell anybody though.