Labor usually starts two weeks before or after the estimated date of delivery.
However, no one knows exactly what triggers the onset of labor. Signs of labor vary from person to person, as each woman experiences labor differently. Labor sometimes begins with amniotic fluid gushing or leaking from the vagina. Women who experience a rupture of the amniotic sac membranes should contact their physician immediately. The majority of women with ruptured membranes go into labor within 24 hours.