When do I tell my work im pregnant?

Hi guys!

I’m 7w3d pregnant & this is my 1st pregnancy. I started a new job the same month I found out I was pregnant. I have yo work minimum 600 hours (almost 4 months) to be eligible for matt leave. Im still not showing and i know its still very early (only a few ppl know so far) Question is when should i tell my work to find a replacement?