When to inform work you’re pregnant

How soon did you tell your boss you were pregnant? I work for a small business where there is one bathroom that I need to use alllll the time. I am 4 weeks and a couple of days today so I don’t imagine I’ll tell my boss until I’m showing but it’s making me nervous about losing my job. I used to live (born and raised) in Canada where this would be no issue (12 month Paid Mat leave) but have since moved to the US. The last person to work at my job was fired after our boss found out she was pregnant and wanted to find a replacement. Anyways that all sounded like a bunch of gibberish but just wondering how others have told their work that they’re expecting and when they let them know?