The cervix is the lower part of the uterus that projects into the vagina. Made up of mostly fibrous tissue and muscle, the cervix is circular in shape. During pregnancy, the cervix lengthens, serving as a barrier.
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 health care provider immediately. The majority of women with ruptured membranes go into labor within 24 hours.