I left earlier than expected from work. I was due to leave 4 weeks before my EDD but I left a month earlier. It was due to stress and the OB wrote a medical certificate for me to cover between my mat leave commencing date and that day he wrote the certificate.
As part of my work's unpaid mat leave policy is that if you leave earlier than 6 weeks before the EDD it is classed as "special mat leave". This means you get paid as per sick leave but your mat leave starts from that date rather than when you had it organised originally. So I am due back a month earlier than planned next year.
I personally think it is a way of diddling me out of mat leave since I was on "sick leave" but oh well... I needed the time off as it has helped me.