Waiting until the end of the first trimester is a social norm but honestly? It's up to personal preference. If you want to tell your boss so that they are aware of why you're not yourself right now but keep it under wraps to the rest of the world until you're ready, go ahead! Just be sure to say something before the third trimester so you can get started on whatever is needed to take leave when the time comes for birth haha
If they are going to be professionally supportive and offer you accommodations you can tell them but if they can’t do anything for you and they’re going to use it against you I wouldn’t say anything just yet.
I let my work know early due to terrible morning sickness at about 8 weeks . It was difficult to get in on time as I was throwing up for ages in the morning 😅