Tell your direct boss first so you can take time off to do check up easier. For colleagues or friends etc,say it whenever you feel comfortable and stable. I only told my boss soon when I found out I\'m pregnant so I could avoid business trip and late meetings.i still didn\'t tell HR and I\'m 5.5 month pregnant now.
need to give a copy of the Dr letter to your HR... so u can get time off to check up with out using your own leave. I told my boss and hr at 6weeks and ask them not to tell others