This study aims to explore biomarkers in the endometrial fluid and tissue of women with moderate to severe endometriosis, with a specific focus on those involved in pre-receptive endometrium and embryo implantation. This research has the potential to uncover diagnostic indicators of impaired pre-receptive endometrium, examine pathophysiological pathways, and identify future targets for therapeutic intervention. Ultimately, the findings may contribute to more personalized fertility treatments, offering new hope for women struggling with endometriosis-related infertility.

Inclusion Criteria:

• Age 18-40 years old
• Diagnosed with moderate/severe endometriosis by ultrasound or laparoscopy (patient group)
• Regular menstrual cycles 28-35 days
• Speak English or Swedish and agree to participate in the study

Exclusion Criteria:

• Pregnancy or lactation in the last 3 months
• Uterine anomalies
• Pelvic inflammatory disease, endometritis, STD
• Gynaecological cancers or other malignancies in the patient's history
• Smoking (more than 10 cigarettes per day) or alcohol abuse
• Immunosuppressing medicines
• Major abdominal or pelvic surgery in the last 3 months
• A specific genetic disease that is diagnosed before PGT in women undergoing treatment

We are going to recruit 30 patients who undergo fertility preservation or fertility treatment before endometriosis surgery in the Reproductive Medicine Clinic in Karolinska University Hospital. Our patients are diagnosed with stage III/IV endometriosis according to rASRM staging by using ultrasound. The control group will consist of 60 healthy women without endometriosis signs in the ultrasound who present to our clinic as oocyte donors or for fertility treatment because of male factor or pregenetic testing for genetic diseases of the partner