When shld you tell your boss about pregnancy?

I told my bosses when I found out I was pregnant so that they allow me to wfh during first trimester or lighten my workload as I was having cramping and all day sickness. I wanted to tell them after my first trimester but my sister advised me to just inform them so they can do necessary arrangement because first trimester is the most crucial period. In case need to carry heavy stuff or work ot etc. :)