I left work at 36 weeks last time, but used annual leave until officially starting mat leave the week of my EDD. I thought that might be too early, but by that point I had SPD, gestational diabetes and the commute was killing me. I also had a million hospital appointments because of the GD, so, frankly, I was very relieved to go off when I did. I was induced at 40+0 so I knew I wouldn't be waiting around for long after my due date either.
This time, if all goes well, I will probably be induced/have an elcs at 37 weeks because it's twins. They advise starting mat leave around 28 weeks with twins but that seems really early! I can work from home, so I'm hoping I can do that full time from 28 weeks (or earlier if I need to), and wait a bit longer to start mat leave, maybe in mid-Jan. But a lot will depend on my health and the babies' health, so it's a lot less predictable.
Good luck to everyone with scans tomorrow!