I think it's totally personal when to start mat leave. I worked to 40 weeks with DS ... Actually shared a trip in the lift with a male colleague on my due date, when he asked me when I was due and I said today, his face was a picture! He couldn't get out of the lift fast enough.
In hindsight that was OK as DS was late, but tough commuting so late on. This time I'll stop a couple of weeks earlier. Prob 38. Since I want to go back for a couple of weeks as stopping at Xmas seems a bit soon.
Who asked about the anti D injection? In all honesty, it is a bit of a stingy one but over v fast and it is better in the arm. They used to give it in your bum and that's just mean ;)