The answer really is... it depends!
We would recommend that in the first 12 weeks of pregnancy you do not take on any new activities, yoga included. In this trimester especially your body may experience symptoms such as nausea and lowered blood pressure which can be exacerbated by the more dynamic classes. If you have been attending regularly prior to conception and would like to continue we'll leave that decision up to you.
From 12 weeks onwards you are welcome to attend classes even if you haven't been before, but you MUST make the teachers aware. Certain postures will be modified, and the amount of the modifications will increase as your pregnancy progresses. We recommend that you sit towards the middle of the room where it is cooler our of the direct line of the heaters and avoid the hotter and more physically challenging classes, that you have plenty of water and most importantly that you listen to your body at all times! When practiced with the proper awareness yoga can be a wonderful support through your pregnancy,