If you're an old hand at the challenges of labor and delivery, you may already be well-versed in recognizing the signs of the beginning of labor. But if you are having your first baby, you're looking at virgin territory, so to speak.
How will you know whether what you're feeling is indigestion or significant contractions? Of course, if your water breaks, this is a pretty definitive indicator that you've moved into the fast lane. If your water has broken, the amniotic fluid will run freely and you won't be able to stop it. You should definitely head to the hospital at this point.
"You should also leave for the hospital if you experience vaginal bleeding or watery/bloody discharge from the vagina; don't feel the baby moving inside you anymore; or experience high blood pressure or persistent stomach pains at any stage of the pregnancy. If there is anything else about your pregnancy that makes you concerned, you should go to the hospital for advice."
http://www.virtualmedicalcentre.com/news/Tell-tale-signs-of-labour/15281