Advanced warning for work colleagues that you 'talk' to, but don't see very often?

I'm 27 weeks and very obviously pregnant. There are people that I deal with via email and on the phone quite often, but only see in person every few months or so. I will eventually have to let them all know they'll have a different internal contact while I'm out on mat leave, but I'm not sure how best to go about it. I've seen one or two recently - one of which seemed very awkward after I caught her quick glance at my tummy! and the subsequent conversation went something like this:

HER: Um, Hello! I just realized it's a been a while since I've been here!
ME: Yes, I guess it has
HER: Um, how are you?
ME: Well, as you can see I'm a bit rounder!
HER: Yes. Well, um.....when?

Perhaps I could've been a bit nicer and helped her out a bit, but gosh it was weird. Makes me think it'd be better to just let people know in an email before they see me, but that just seems so personal and me, me, me when I'm clearly corresponding with them on work related matters.

any advice? Am I overthinking it??

Re: Advanced warning for work colleagues that you 'talk' to, but don't see very often?

Nah, avoidance is my number 1 method as well

With DS, for anyone with whom I had an 'email' relationship with I just began making mention of "when I'm out" about 2 mos before I went on leave. I did try to get to everyone within a month before just so I didn't just up and disappear on them (most of what I do is over email - all international work) but I've had that extremely awkward conversation myself. Usually in the bathroom