This study is a multi-center, prospective, observational clinical trial study. 510 full-term pregnant women will be enrolled as subjects, and the ratio of eligible subjects in the two groups is 1:1. In the cesarean section group, full term pregnant women with one prior cesarean section after spontaneous labor who are willing to try the trial of labor after cesarean (TOLAC) and in accordance with the criteria according to the 2016 China vaginal birth after cesarean (VBAC) clinical management guidelines will be enrolled and recorded by our homemade registration form of TOLAC. In the non-cesarean section group, pregnant women after 37 weeks of gestation after spontaneous labor but without vaginal labor contraindications will be enrolled. After spontaneous labor for 24h, their final delivery mode will be recorded. In the following 42 days postpartum, their complications and the neonatal outcome will be followed up.

Inclusion Criteria:

1. Volunteers sign the informed consent
2. Age: 20-40 years;
3. Singleton, a cephalic presentation;
4. No contradiction to vaginal delivery; 5.39~42 weeks; 6.Spontaneous labor

Exclusion criteria:

1. Konwn contraindication to vaginal delivery or severe complications;
2. Multiple gestation;
3. Uterine malformation;
4. Severe psychiatric disorder;
5. Without family's support.

In the cesarean section group, the extra inclusion criteria includes: Only one prior low transverse uterine incision;Extra exclusion criteria:1. With mutiple history of c esction;2. Prior extensive transfundal uterine surgery, such as for fetal surgery, myomectomy, or uterine reconstruction; Prior classical vertical uterine incision, or an inverted "T" or "J" incision;3. Short interpregnancy interval;4.Prior uterine rupture or dehiscence, or cesarean scar pregnancy;4.Evaluated fetal birth weight> 4000 g.

In the non-cesarean section group, the extra criteria should include: nulliparous