I worked up to 34 and 35 weeks with my two as it coincided with holidays, but I could have kept going if I needed to. I teach secondary PDHPE, so sitting down is a luxury that doesn't come too often and the heat was hard to deal with - but I made it. This time I intend on working up to about 37 weeks - all going well. It really depends on so many things and you can't really tell how you will feel until the time comes around. You can always alter your leave form as the time draws closer if you really need to and we do have generous sick leave entitlements that you can take advantage of. I would say leave it as 36 weeks and alter it if you need to. If you are medically not making it you can be on sick leave with a Dr certificate up unitl mat leave starts, which doesn't have to be until your due date. Good Luck.