Tricking someone into pregnancy

So one of my closer friends is tricking her fiancé into getting her pregnant. She's telling him she's taking birth control when it's prenatal vitamins and some natural supplement to try and help her chances. I don't talk to him much even when we hang out so I don't know how to approach it. I feel like I need to tell him, and she sees nothing wrong with it. He was pushing her to birth control because he enjoys cumming in her but he doesn't want a baby right now. Help meeee!