I recently discovered that green tea and black tea come from the same bush, it is just the process to make them into tea leaves that is different! The amount of caffine depends on how you brew it and how long you brew it for, but generally they are comparable.

I had green tea when preg, but limited my intake to one a day. And enjoyed caffine free teas at other times. T2 make a sensational honey and green almond tea that is caffine free, made from the leaves of an almond bush i think!