I started at 35wks 4days and had DD at 36wks3days so 6days later. I think 30weeks would be good even earlier if you could and want. One of the ladies I work with went of at 26weeks (she is a midwife) didn't know you could go that early so next baby I have I will be looking at going early probably between 28-32weeks. I think in the public health sector where I work under 34weeks you need a dr's certificate which generally isn't hard to get to commence mat leave.