Need some advice

I'm currently 6w5d and working in a contract position. My contract just got extended through the end of the year (I'm due in November), but I have 2 different interviews at the same company I'm contracted at for full time roles. No one knows about my pregnancy, when do I need to tell them? Am I ethically obligated to be more upfront as soon as I interview or is it ok to wait until I would have shared the pregnancy under different circumstances? Thoughts?