I'm glad to hear you have a sensible and responsible attitude to your unborn child, so many women are selfish and keep on tokin and drinking even though it's been proven to be harmful. How long since you last toked and your build and metabolism are all factors so unless I have that info it would be useless to even speculate.
On average three months is enough time for cannabis to be completely out of your system so if it's been longer than that you should be fine, if they do find traces it is (IMO) best to be honest and just tell them you were toking but you stopped for your unborn child, I think most medics would respect that more than if you tried to blag it.