Vacuum extraction is an important assisted vaginal operation in the second stage of labor. The placement of the cup over the flexion point, about 3 cm anterior from the posterior fontanelle, is critical to the success of a vacuum extraction. Perform vacuum extraction intermittently along with the uterine contraction, and it should be abandoned if the vacuum cup detaches more than 3 times or descents not occur after 3 times of uterine contraction; the total time of operation limits 20 minutes.