There was a discussion elsewhere about this but it was off-topic
What do people think about Teyla's decision to stay on active duty while pregnant? although I think John was right to bench her, I cannot fault Teyla for wanting to keep fighting. She may think that the best way to protect her baby is to keep it safe from the wraith and replicators, and that the rest of the team are more likely to achieve that with her help. She could argue that if the replicators or wraith overrun Atlantis, then her sitting comfy while John and Ronon were off doing the fighting, won't have done her baby a great deal of good.