At 13-14 weeks other people started to notice. I told work at 15 weeks and they were not surprised. Of course, I started this pregnancy looking about how I did at 16 weeks with DS... and now I look at least a month larger than I did at this time with him. Sigh.
I could tell around 8 weeks. It became noticeable to others last week at 13 weeks mostly because I have switched to all maternity clothes. With Kayley, I didn't start exclusively wearing maternity until 15 weeks.