Abstract Study question To investigate if serum AMH concentration variations are correlated with protein expression in follicular microenvironment affecting IVF outcomes. Summary answer Serum AMH concentrations were associated with altered levels of intrafollicular protein involvement of the complement pathway in immunity response in follicular fluid (FF). What is known already Anti-Müllerian hormone (AMH) plays a crucial role in regulating growth and development of ovarian follicles. The follicular fluid is produced during folliculogenesis and contains a variety of proteins that play important roles in follicle development and oocyte maturation. AMH concentration in follicular fluid can be a marker of ovarian reserve status and oocyte competence. AMH elevated levels may indicate a higher ovarian reserve and are sometimes associated with a greater ovarian response to ovarian stimulation used in IVF. However, the exact relationship between AMH levels in follicular fluid and IVF outcomes may vary among women and depend on various factors. Study design, size, duration The study included FF collected from 75 patients underwent IVF from December 2018 to June 2019.All patients enrolled underwent GnRH antagonist stimulation protocol with r-FSH according to clinical/ovarian features.Patients were sorted into three groups according to serum AMH concentrations: AMH≤1.0 ng/ml, n = 25 (A group); AMH=1.1-2.0 ng/ml, n = 29 (B Group); AMH>2.0 ng/ml, n = 21 (C group).Cutoffs for defining low(A), average(B), and high(C) AMH serum concentrations corresponded to round values of 30th and 70th centiles of each measurement. Participants/materials, setting, methods Exclusion criteria: endometriosis, metabolic/endocrinology diseases and oligoasthenoteratozoospermia. FF aspirates from individual follicles (diameter ≥18 mm) were collected on the day of oocyte retrieval. The FF was analyzed by two-dimensional gel electrophoresis (2-DE). Oocyte number and quality, fertilization rate are IVF outcome measures. Data were analyzed using the unpaired Student’s t-test by IBM SPSS-STATISTICS versions 20.0 and considered significant if p-value ≤ 0.05. Main results and the role of chance 180 protein spots were highlighted in three groups: 80% is represented in all the samples analyzed, whereas 19 protein spots out of 180 are group-specific. Five unique upregulated proteins were identified in the A group and five in C group respect to control group (B). These were identified IG, CO4, ALBU, TRFE, IGLC in A group, while A1AT, ANT3 A2HS, HPT and CO4 in C group. A and C group showed worse oocyte quality associated with a lower fertilization rate than B group. On the basis of the proteome analysis, the component of the complement cascade C4 was found more plentiful in patient with low and high AMH serum concentration compared to average AMH serum concentration ones. The presence of high levels of the unprocessed precursor C4 correlated to serum AMH fluctuations is an indication of non-activation of the complement pathways fundamental for follicle maturation and ovulation compromising IVF outcome. Limitations, reasons for caution Limited number of patients. Age and lifestyle factors (i.e. smoking, diet) are not considered. Wider implications of the findings Results showed an increase of CO4 in FF of patients with low and high AMH serum concentrations. CO4 FF high levels could be indicative of defective complement activation during ovulation with consequent impaired processes and lower standard oocyte competence. Thus, CO4 could be identify as biomarker to predict IVF success. Trial registration number Not Applicable