Letting your employer know

I have a practical doubt.

When its the best time to let your employer know that you are pregnant?

I was permanent and more stable in my previous job but now im not really sure where i stand and how to proceed here.

I know the law and my rights as a pregnant woman. I just dont know the best time to let work know.

Im going to get my documentation on the 23 hopefully boletim and all. How did u do it? And when?

Thank you