Thanks ladies... my instructor says it's safe considering I have been doing it for a while now and also knows alternatives for moves which arent safe in pregnancy...however, she has also said, if I am at all worried, and given my history, it's fine to resume after the first trimester.
My friend teaches pregnancy yoga classes and she advises starting them after 12 weeks.
I am weighing things up...I want to try and keep my anxiety levels under control this time, and yoga is one way I can do that, perhaps I will do a very modified reduced practice at home for a while, and resume normal classes if I am blessed enough to make it past 12 weeks this time round.