Pre-natal Yoga Anyone?

I spoke to a pre-natal instructor last week about Yoga. What she had said was that it is good to take it towards the end of the pregnancy to make your body ready for delivery and when you can no longer do your regular activities. I spin, so the way I took that was when spinning is no longer comfortable, go to the yoga.
When I was in my first trimester i took regular yoga and i know that you can do the back poses until into your 4th month. Hope this helps:)