This is usually the first day of your maternity leave. You do not have to be actually at work to have this choice. For example, you might be off sick. If your employment ends before the start of the 11th week before the week your baby is due, your SMP will start at that 11th week. SMP can be paid for up to 39 weeks, this is called the Maternity Pay Period (MPP). Statutory Maternity Leave.