Now that you say that, I can see both happening as well. Polaris making a desperate gamble to get out the prison, for not only her safely, but her child's as well, and then finding out later that she had already lost the child when she returns to the Underground.
Or she never really was pregnant, like some people have suggested, and people were just trying to give her incentive to turn against her friends. We'll just have to wait and see.