IPUS group women were performed pelvic examination at admission and every 2 to 4 hours during the first stage of labor and at least hourly during the second stage by intrapartum ultrasound.

VE group women were performed pelvic examination at admission and every 2 to 4 hours during the first stage of labor and at least hourly during the second stage by vaginal examination.

In IPUS group, the patient's labor was observed by intrapartum ultrasound.

Medical record about the length of first stage of labor

Medical record about the length of second stage of labor

physiological parameter about the body temperature when the patient has fever

clinical assessment about the soft birth canal laceration after labor, including I(Perineal skin and vaginal entrance mucosa laceration, little bleeding）, II（The lacerated injury has reached the fascia and muscle layer of the perineum, involved the mucous membrane of the posterior wall of the vagina, extended to the groove on both sides of the posterior wall of the vagina and tore upward, the anatomical structure is not easy to identify, and there is more bleeding）,III（The lacerated wound extends deep into the perineum, the external anal sphincter is broken, and the rectal mucosa is intact）, IV（The anus, rectum and vagina are completely penetrated, the rectointestinal cavity is exposed, the histological tissue is seriously damaged）

total postpartum blood loss in 24 hours measured by weighing method