Abstract Study question Does the concentration of amphiregulin in the follicular fluid affect oocyte maturation and embryo quality in patients with polycystic ovarian syndrome? Summary answer The concentration of amphiregulin affects oocyte maturity and embryo quality in patients with polycystic ovarian syndrome and can be used as a predictive biomarker. What is known already Polycystic ovary syndrome (PCOS) is a common metabolic dysfunction and heterogeneous endocrine disorder in women of reproductive age. Epidermal growth factor receptors and their ligands, such as amphiregulin, which are expressed in female reproductive tissues, have been shown to regulate various important reproductive functions. Amphiregulin is reportedly involved in oocyte maturation through autocrine and paracrine mechanisms, however, the impact of amphiregulin on oocyte maturity end embryo quality in patients diagnosed with POCS which goes under controlled ovarian stimulation remains unknown. Determination of potential biomarkers might be the key to successful IVF outcomes. Study design, size, duration The study consisted of a total of 87 oocytes obtained from 30 patients who underwent ICSI at UKS Homburg (Germany) between October 2021 and March 2022. Fifteen patients were diagnosed with polycystic ovary syndrome while the other fifteen were fertile without any diagnosis. For the study purpose, follicles were aspirated separately, and the follicular fluid was centrifuged for 5 min at 1,500×g. After the preparation, the supernatant was removed and stored at -20 °C until analysis. Participants/materials, setting, methods Concentrations of amphiregulin in follicular fluid were determined by using a commercially available sandwich ELISAkit (Duo Set; R&D Systems Inc., Minneapolis) in accordance with the manufacturer’s instructions. Good embryo quality (GQE) on day 3 was defined as a 7-9 cell stage embryo with less than 25% of fragmentation and with equally sized blastomeres. Between-group comparisons were conducted with a Mann-Whitney test. Logistic regression analysis was used to determine the influence of amphiregulin on studied parameters. Main results and the role of chance The mean age of all patients was 33.5 (±5.2) years. Patients included in the study were stimulated according to a gonadotropin-releasing hormone (GnRH) antagonist protocol. Out of the 87 oocytes, 59 (67.8%) were at MII stadium, 13 (14.9%) were at MI and 8 (9.1%) were at GV stadium. ICSI was done only with MII and MI oocytes and the fertilization rate was 70.1% (61 oocytes were fertilized out of 72). Obtained results showed that concentrations of amphiregulin were significantly lower in follicular fluid of PCOS patients [(107.00(51.95-131.00) ng/mL vs 115.27(43.19-209.51) ng/mL) respectively; p = 0.024]. Data comparisons between mature and immature oocytes indicated that amphiregulin concentration was significantly higher in follicles where mature oocytes were developed [(117.50 (65.99-209.51) ng/mL vs 81.75(43.19-128.20) ng/mL) respectively; p < 0.0001]. Additionally, logistic regression analysis confirmed the positive effect of amphiregulin concentration on oocyte maturity (p < 0.001). Out of the 61 fertilized oocytes, 36 (59.0%) formed good-quality embryos. Additional analysis indicated that oocytes that developed into good-quality embryos came from follicles where amphiregulin concentrations were significantly higher compared to those that developed into poor-quality embryos [(124.05 (91.88-209.51) ng/mL. vs 86.72(43.19-109.40) ng/mL) respectively; p < 0.001]. Logistic regression analysis confirmed the positive effect of amphiregulin concentration on embryo quality (p < 0.01). Limitations, reasons for caution The limitation of the presented study was the relatively small patient cohort. Although the pregnancy rate in the presented study was 27.8 % , single embryo transfer was not performed, therefore further research should link amphiregulin concentrations with the pregnancy rate as well. Wider implications of the findings Results obtained in the study might be useful for further handling of PCOS patients since the literature already confirmed that PCOS patients produce an increased number of mature oocytes, so culture medium-containing amphiregulin might be a future solution for those patients. Trial registration number 146/19