Abstract text Endoscopic management of the unexplained infertility, what does it add? Stephan Gordts stephan.gordts@lifeexpertcentre.be Unexplained infertility “strictu sensu” is not a diagnosis, but a description of a status where no causal factor is identified in a couple trying to conceive for at least one year. The more parameters are assessed, the more likely to identify an etiology, the less likely becomes “unexplained” infertility. Limiting the fertility exploration to indirect visualization techniques like ultrasound, HSG or HycoSy involves the risk of missing existing pathologies. Uterus Uterine volumetric abnormalities can be detected by indirect techniques, but information is lacking on the visualization of the endometrium in case of chronic endometritis and the presence of endometrial defects and hypervascularization areas as seen in patients with adenomyosis. Tubo-ovarian Even with the increased accuracy of indirect visualization techniques, lesions of minimal endometriosis and tubo-ovarian adhesions are not detected (Table). Tubal normality constitutes not only normal tubal patency but also normal tubal function. The importance of subtle tubal lesions is underestimated. Hydatid of Morgagni are detected in 38.1% in patients with infertility versus only in 16,7% in fertile women (Gupta et al. JMIG 2017).Removal of these lesions resulted in a spontaneous pregnancy rate of 58.7% versus 20.6 in the non-treated group (Rasheed et al. EJOG Repr. 2011). Endometriosis In a series of 107 patients with unexplained infertility and 3 failed IVF cycles (Agni Pantou et al. J. Clin. Med. 2019)laparoscopy revealed the presence of endometriosis in 57.97%, peri-adnexal adhesions in 23.3% and was normal in 18.69%. Also, in a group of patients with 3 failed IVF cycles and unexplained infertility (Xiaoming Yu et al.Medicine 2019) laparoscopy showed endometriosis in 57.7%, tubal abnormalities in 31.1% and adhesions in 33.3%. Laparoscopic correction of these pathologies did not only result in a spontaneous pregnancy rate of 35% but resulted also in a higher pregnancy rate after IVF compared to the non-treated control group. Unexplained infertility hides frequently undiagnosed endometriosis. Endometrial BCL6 levels, a proto-oncogene where overexpression is associated with increased cellular proliferation and progesterone resistance, are increased in patients with endometriosis. In case of elevated BCL6 in patients with unexplained infertility, laparoscopy confirmed the presence of endometriosis in 93.8% (Evans-Hoeker et al. 2016). Abnormal BCL6 expression in a population with unexplained infertility reduced the chance of having a successful IVF treatment in 74% of the population (Almquist et al. Fertil Steril 2017). Transvaginal Hydro Laparoscopy Direct endoscopic visualization remains important but due to the invasiveness, diagnostic standard laparoscopy is frequently postponed or omitted in the exploration of the infertile patient. The technique of transvaginal hydro-laparoscopy allows in a minimal invasive way the inspection of the pelvis. In a consecutive series of 2288 patients without obvious pelvic pathology, findings were normal in 49.3%, endometriosis was diagnosed in 15.9% and tubal pathology in 14.5% of the patients (Gordts et al. FVV 2021). The rate of failed access was 1% and the complication rate 0.74%. Causing a minimal ovarian trauma, treatment of these early endometriotic lesions resulted in a spontaneous pregnancy rate of 73.2%. Conclusion The inappropriate use of “unexplained infertility” by omitting the diagnostic endoscopy in the exploration of the infertile patient, can hide undiagnosed and treatable pathology, jeopardizing possibilities for patients for a spontaneous conception and can be responsible for reduced pregnancy rates after IVF.