It can be. Some women experience diarrhea as their body prepares for labor, but this can happen several weeks before you actually go into labor (or, yes, just a few hours!). You shouldn’t assume that having diarrhea in the third trimester means you’re going into labor soon, but if the diarrhea occurs alongside other symptoms of labor—like increased contractions and loss of mucus plug—then it could be a sign that labor is about to start for real.