Stages of parturition. (a) Parturition has not yet begun. (b) The cervix is dilating. (c) The cervix is completely dilated, and the fetus’s head is
entering the cervical canal; the amniotic sac has ruptured and the amniotic ﬂ uid escapes. (d) The fetus is moving through the vagina. (e) The
placenta is coming loose from the uterine wall in preparation for its expulsion.