I did ante natal aqua aerobics and swam right up til a few days past my EDD..... floating around was such a relief on my tired body! I believe it's fine anytime up til when your waters break. Enjoy
I did too. I did go in to labor mid aqua class though, but it was all good, awesome pain relief even though the physio was a bit scared! tehehe

ETA: I should qualify that. I was 3 days overdue so would have gone in to labor anyway, it wasnt the aqua class. I did 2x per week classes from 12 weeks for both of my pregnancies, on my midwife and GPs recommendation.