Telling my in laws

My fiancé and I are NTNP (not trying, not preventing for those that don't know). His parents are very religious Christians and from a different culture, and don't believe in having kids before marriage. We are getting married next year, but I have a feeling I'm pregnant again. My period isn't due for another five days but I just have that feeling of "knowing". I'm wondering how I should tell them, if I am pregnant. His mom is literally going to flip out. I'm just super anxious about it, even though I don't know for sure yet. If it happens before our wedding, I just feel like she's going to have forever disapproval of me. We have had a tough relationship in the past and she is just starting to come around and get along with me. I'm afraid this is going to ruin that.