When did you tell your school you were pregnant? My coursework calendar runs into next year

Second pregnancy, early days. I teach IB diploma, and the internal assessment calendar for my classes runs well into next year with my name on every deadline. Part of me wants to tell my coordinator now so cover can be planned properly. Part of me wants to wait until I'm further along. Last time I was at a different school and only told them when I started showing, which caused a scramble I'd rather not repeat. Teachers especially: when did you tell, and did telling early change how you were treated?