Just another opinion from the other side of this (massively outing but never mind). I used to be a wedding singer. I got pregnant with DD with a whole summer of weddings ahead of me, and made the choice to mention it all my couples once I got to about 25 weeks.
This was mostly because of my personal experience of 5 years of infertility and IVF trying to conceive DD - I knew that if I had been going through that when I got married and my wedding singer turned up unexpectedly heavily pregnant I would have found it hugely upsetting if I'd not had time to prepare myself (not going into the whys or wherefores of this, it's just a fact).
Not saying other wedding suppliers should do this, just my choice. I took DH with me as my roadie for the later gigs to make sure I was never on my own, and always had a plan B.
My last wedding was at 34-35 weeks, booked over a year before I got pregnant. I told the couple early on, gave them the option to cancel as I understood they might be a bit nervous - I was due to be with them the whole day and sing during their ceremony, meal and first dance/evening party. They insisted they were fine to go ahead if I was, didn't want to cancel etc.
The day came, I finished up the ceremony, went to the toilet and my waters broke
. Started contractions, had to leave and go to hospital and DD was born around 4 hours later. The couple were so so lovely about it and thankfully I'd planned back-up playlists for the venue and DJ to use in the event of something happening, but it wasn't how I planned my last gig to go!
Obv not saying that you're obliged to disclose pregnancy (or that all pregnant wedding suppliers will go into early labour) but it can happen
.