1. To describe the average labor curve and establish new labor progression standards.
2. Cesarean section rates: Based on big data, the investigator will introduce the international advanced Robson class method and identify the appropriate level of cesarean section rate for each type population.
3. Establishment of "Chinese maternal-fetal medical collaboration network" and APP to promote natural childbirth.

1. To describe the average labor curve and establish new labor progression standards. The investigator will investigate the current characteristics of obstetric population and the labor progression with obstetric intervention in China. The investigator compare the different effects of traditional labor progression management model, new labor progression management model and active labor progression management model on labor outcomes. Based on the best outcomes of maternity and infants, the investigator will establish and modify new labor progression which is suitable for Chinese.
2. Cesarean section rates: Based on big data, the investigator will introduce the international advanced Robson class method and identify the appropriate level of cesarean section rate for each type population.the investigator compare cesarean section rates of different level hospitals and evaluate the effects of reducing cesarean section rates. The investigator also analyze the risk factors of cesarean section rates of the ten Robson classification, which will provide basis for reducing cesarean section rates under the new strategy.
3. Establishment of "Chinese maternal-fetal medical collaboration network" and mobile application software (APP) to promote natural childbirth: The investigator establish perinatal data center using the hospital information system (HIS) system of hospital. The investigator predict the cesarean section rates and relative factors using the Robson classification method, and propose the new strategy of reducing cesarean section rates. Meanwhile, the investigator develop the quality management system toolkit which can help clinicians standardize behavior and improve obstetric safety.

Inclusion Criteria:

1. Chinese pregnant women
2. singleton
3. head position
4. 37 weeks + 0 day - 41weeks + 6 days
5. primipara
6. low-risk pregnancy
7. vaginal delivery willingness
8. vaginal cervix <7 cm after labor

Exclusion Criteria:

1. multiple pregnancy
2. non-head position
3. stillbirth
4. selective cesarean section
5. prenatal cesarean section
6. age <18 years
7. previous childbirth history
8. pregnancy complications
9. important fetal malformations.

A total of 20 hospitals from different places of China participated this study. Their annual delivery amount are more than 5000 times and their cesarean section rates are about 40%. The labor progression study include a total of 15,000 puerperae.

There are 20 hospitals participated this study, we need get their agreement to share data.