In women with a mature uterine orifice, the uterine orifice usually opens up within 12 hours after the placement of the hydrosac. However, if the cervix is less mature, it usually takes 12-24 hours for the opening of the uterus to occur. The time of opening of the uterine orifice is related to the condition of the uterine orifice itself. Under normal circumstances, if the uterine orifice is mature, i.e. soft and short cervical canal, the induction of labor by water bag should take about 6-8 hours, and most of them can open the orifice within 12 hours. However, for pregnant women with poorly mature cervix, i.e. with hard orifice and long cervical canal, the opening of the uterus should be gradually opened within 12-24 hours. Usually the water sac comes out naturally after the opening and enters into labor, regular contractions can occur and the fetal sac is expelled within 12 hours. If the opening of the uterus is still not opened 24 hours after the hydrosac, it is usually judged that the hydrosac has failed to induce labor. In addition, we should pay attention to the abdominal pain, fetal heart monitoring and fetal movement after placing the hydrosac. If the hydrosac is placed for more than 24 hours without any uterine contraction, the hydrosac should be removed in time to avoid infection.