The Role of Probiotics in the Treatment of Endometriosis (ProMetrioS): a Randomised Double-blinded Placebo-controlled Cross-over Trial

Patients will be recruited among the outpatient population of the National Center for Endometriosis, Department of Gynecological Surgery and Urology, Gynecology Department, University Hospital Center Zagreb following the inclusion and exclusion criteria.

To participate in the study all patients will be required to sign the Informed Consent form.

All patients will undergo a complete anamnesis via a digital form to investigate their lifestyle (occupation, stress, diet, physical activity level).

The study period will be 6 months: eight weeks on either option (verum/placebo), with an eight week washout period in between. The purpose of the washout period is to allow the gut microbiome to return to baseline. The washout period was determined based on previous gut microbiota studies with a similar design (reference), based on the fact that the gut microbiota can change rapidly (\< 7 days) r.

The outcome measures (gut microbiome, quality of life) will be assessed in four distinct time points in context of the planned intervention.

T1 - before the intervention (start-of-study)

T2 - after the first intervention cycle/phase 1 (verum/placebo) of two months

T3 - after the wash-out phase of two months

T4 - after the second intervention cycle/phase 2 (verum/placebo) of two months (end-of-study)

Stool sampling will be performed with the aid of specific kits indepently by the patients. Lifestyle and quality of life will be evaluated by an online form designed specifically for the purpose of this study in Microsoft Office Forms (Microsoft, San Francisco, USA), short Online Form.

Through the process of randomization, patients will be allocated to either first receive the verum (probiotic) or the placebo (maltodextrin), and second the placebo or verum inversely.

Both patients and researchers involved will be blinded (double-blind study), the patients will be informed that they are going to take a probiotic twice for two months with a two-month time division. The intervention will consist of treatment with a multistrain probiotic formulation (Omni Biotic Stress) and the placebo which is identical in all its characteristics and packaging. Patients will be instructed to consume one sachet a day of each (probiotic) for 8 weeks and to report any symptoms or side effects related to its use. Adherence control will be carried out through the patient's notes on a separate online form provided, and also by checking the number of sachets used.

Since this is a cross-over study, data will be compared between time-points T1 and T2, and time-points T3 and T4, with the goal of minimizing the potential effect if we find that the effect of the probiotics lasted longer than eight weeks in those randomized into the intervention arm first.

• Change in quality of life measured by EHP-5 questionnaire [Срок оценки: Week 1, Week 8, Week 16, Week 24 (6 months)]
• Change in quality of life measured by SEQOL questionnaire [Срок оценки: Week 1, Week 8, Week 16, Week 24 (6 months)]