Mode of delivery affects the success rate of assisted reproductive techniques (ART). In this case study, the investigators will evaluate changes in the bacterial ecology and inflammatory markers of the female uterus with different delivery modes. We will investigate whether the dominate endometrial microflora is interrupted by the Cesarean section in the infertile women undergoing ART, and the potential mechanism will also be further explored prospectively.

The highly prevalence of cesarean section rate in China had drawn great attention world widely. Post-cesarean section scar diverticulum ( PCSD) is a poor healing of the local incision after Cesarean section which happened in19.4%~88% of patients. The cavity is formed by the original incision connected with the uterine cavity. Patients with diverticulum are often accompanied by prolonged menstruation and uterine effusion, which may accompany with endometrial inflammation and impair embryo implantation rate.

Though Cesarean section plays an important role in the treatment of dystocia and also decreasing perinatal mortality, it may impact natural conception and the success rate of ART in secondary infertile patients. Data from other researchers have revealed that Cesarean scar may related to poor pregnancy outcome during ART treatment. We have retrospectively analyzed the pregnancy outcome of ART treatment in patients who have had live birth previously from January 2014 to May 2018. The biochemical pregnancy rate, embryo implantation rate and clinical pregnancy rate are all lower in patients with Caesarean section compared to patients after natural labour, the clinical data is even worse in patients with PCSD. The results suggest a close correlation between the outcome of assisted reproductive therapy and the uterine condition. Further evaluations are required related to whether the dominate endometrial microflora is interrupted by the Cesarean section in the infertile women undergoing ART, and the potential mechanism will also be explored accordingly. A single-center, prospective, case-control study will be carried out.

Inclusion Criteria:

1. Women age ≥20 years and ≤40 years.
2. infertile Women with previously live birth.
3. Previous failed transfer cycle ≤2
4. Didn't participate in other clinical subjects within three months.
5. Written informed consent.

Exclusion Criteria:

1. surgery history including: Ovariectomy, myomectomy, adenomyomectomy.
2. Uterine diseases including: uterine malformation, submucosal uterine fibroids and intrauterine adhesion.
3. One of couple has abnormal karyotype.
4. Recurrent abortion ≥2.
5. Untreated hydrosalpinx.
6. History of tuberculosis (pulmonary tuberculosis, pelvic tuberculosis etc.).

Infertile patients who had live birth previously and met the criteria, required for IVF treatment from Aug 2019 to Aug 2022 in our center.