To evaluate the endometrial and isthmic microbiota in patients with isthmocele after C-Section, and if this microbiota is similar or not with better reproductive outcomes.

A total of 45 subjects undergoing in vitro fertilization treatment. Fifteen patients without isthmocele will be included in the control group and 30 patients affected with isthmocele in the other group, divided in 2 subgroups: 15 with 1 previous C-Section, and 15 with 2 or more previous C-Section. Paired samples of endometrial fluid (EF) and isthmic fluid (IF) will be obtained simultaneously the day of egg retrieval. Patients will follow a protocol for all-freezing embryos or oocytes.

Inclusion Criteria:

1. Patients with isthmocele:

   • Patients performing IVF treatment with a planned cycle segmentation and consecutive frozen embryo transfer on a hormone replacement therapy (HRT) cycle or natural cycle.
   • Age between 18 - 45 years all (both inclusive).
   • One or multiple C-sections.
   • Isthmocele present during TV scan.
   • BMI: 18,5 - 35 kg / m2 (both inclusive).

2. Patients without isthmocele:

   • Patients performing IVF treatment with planned cycle segmentation and who would have embryo transfer with frozen embryos under hormone replacement therapy.
   • NO Isthmocele present during transvaginal ultrasound.
   • BMI: 18,5 - 30 kg / m2 (both inclusive).

Exclusion Criteria:

• Age < 18 and > 45 years old.
• Previous or active endometritis.
• Patients who are IUD carriers for the last 3 months.
• Patients who have taken prescribed antibiotics in the last 3 months previous to sample collection.

Female patients undergoing IVF treatment.