I work in a small office of mostly females (one part-time male). Last year, they were extremely supportive with time off when I had my miscarriage, and I hadn't even been far enough along to tell them I was pregnant.
I had great blood results last weekend, and will have a u/s Monday. I'm tempted to tell the boss on Monday if the results are good I've thought about giving her a heads up, just so she is aware if I am tired or moody (or if the dreaded m/s hits full force some day). However, we're under a lot of stress--our secretary is out recovering from surgery and we're not yet sure if she'll be back next week, the boss is leaving next week for a week-long overseas conference, and then right when she gets back she'll have 2 visiting delegations back to back (I work in a university study abroad office). It's unlikely that the office will calm down much before May--would you recommend telling her now, or simply waiting it out when I'll be close to 2nd tri anyway?
Re: When to tell the boss?
It's definitely a personal decision, and it's great that your office was so supportive when you needed them last year. However, given everything that is going on right now, I'd probably wait to tell them. I told work at 13 weeks, after we heard the h/b on doppler.
You mention that your office won't calm down much until May. That isn't that far off. Of course, if you anticipate needing a lot of time to run to doc appts and/or bloodwork, you may be better off telling up front since things will be so busy. Your call.