Effect of follicular flushing on oocyte retrieval rate and the quality of embryos derived from index oocytes: a prospective cohort study

Objective: To investigate the effect of follicular flushing on the number of oocytes obtained from patients by isolating the oocytes obtained from the first aspiration and only flushing in separate groups, and to investigate the potential damages of flushing application on the embryo by comparing the quality of the embryo developed from the oocyte obtained as a result of flushing with the group without flushing. Materials and Methods: Within the scope of a prospective cohort study, all patients who underwent OPU by a single clinician after controlled ovarian hyperstimulation at the Akdeniz University Assisted Reproductive Treatments Center between June 2021 and June 2022 were included in the study. The study was designed to examine only a single follicle of each patient, and immediately before the OPU procedure, the first accessible follicle over 12 mm in any ovary was determined as the index follicle, and its dimensions (height x width x depth) were measured and recorded in millimeters. During the OPU procedure, the entire amount of pure follicular fluid was delivered to the IVF laboratory for initial evaluation, and the amount of fluid and the presence of COC were recorded. If COC was not observed in the first sample sent, an additional flushing procedure was performed. The additional sample obtained after the flushing-aspiration procedure was delivered to the IVF laboratory, and the presence of COC was reinvestigated. Each oocyte was individually followed up after ICSI, and group comparisons were made for each stage according to whether oocytes were obtained in direct aspiration or after flushing. Results: COC was obtained in the first aspiration in 336 (39.5%) of the total 850 patients, and COC was obtained as a result of the flushing procedure in 267 (31.4%) of the 514 patients who did not initially obtain COC. In 247 (29.1%) patients, no oocytes were obtained. In the analysis conducted to examine the effect of follicular flushing according to percentile subgroups, follicular flushing 58 significantly increased COC retrieval in all percentile subgroups. In the ≤10 percentile subgroup, the success of COC retrieval per follicle after the first aspiration was 24.2%, while this rate increased to 55.8% after the follicular flushing procedure. The same success rates increased from 36.5% to 73.3% in the 11-49 percentile subgroup; from 45.2% to 72.4% in the 50-89 percentile subgroup, and from 45.1% to 71.4% in the ≥90 percentile subgroup, and all these increases were statistically significant (p=0.001). In the obtained results, while a total of 336 COCs were obtained from 850 follicles in all patient subgroups in the first aspiration, an additional 267 COCs were obtained with the application of follicular flushing. While equal amounts of COC were obtained in the first aspiration in the 50-89 and ≥90 percentile subgroups; when flushing was performed on follicles where no COC was obtained, higher COC retrieval rates were found compared to the first aspiration in the ≤10 and 11-49 percentile subgroups (p=0.016, p=0.01, respectively). According to the analysis conducted to examine the effect of follicular flushing on MII oocyte, 2PN, D3, and D5 moderate-good quality embryo retrievals, there was no statistically significant difference between the first aspiration group and the flushing group (p>0.05). However, in the binary regression analysis where significant factors among subgroups such as age, BMI, trigger type, maximum follicle diameter on the trigger day, and the total number of follicles over 17 mm in the ovary of the patient were evaluated within the same model; it was shown that MII oocyte, 2PN, moderate-good quality D3, and D5 embryo retrievals were not adversely affected by flushing in any percentile group. There was no significant difference in β- hCG positivity, clinical pregnancy, and live birth success rates between the group where oocytes were obtained in the first aspiration and the group where oocytes were obtained in flushing. Conclusion: The application of follicular flushing significantly increases the number of oocytes obtained in all follicle sizes. Especially in follicle volumes below 6 cc, significantly higher oocyte retrieval is achieved with flushing compared to aspiration only. There is no significant difference in the detection rates of MII oocytes, 2PN, moderate-good quality D3, and D5 embryo development from the obtained oocytes. This situation proves that the follicular flushing application does not harm the obtained oocyte. Keywords: OPU, Oocyte Retrieval, Follicular Flushing, Oocyte Yield, Embryo Quality