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Abstract Study question The study is to compare cumulative pregnancy rates of embryos transferred with and without spent culture media to confront biofeedback’s role in clinical outcomes Summary answer Transferring the blastocysts with spent culture media improved the pregnancy rates. Biofeedback was observed from the blastocyst stage. The blastocyst freezing and transfer approach improved. What is known already Biofeedback is often encountered in regulating menstrual cycles and other events in continuing gestations with estrogen, progesterone, beta hCG..etc. A similar biofeedback is possible with growing blastocyst for implantation. Since the in-vitro culture of embryos is devoid of its occurrence, it may lead to asynchrony of subsequent events and implantation. There is no scientific evidence from metabolomics on the characterization of these substances or secretions from spent culture medium that includes cell-free DNA giving feedback and its role in improving clinical outcomes. Study design, size, duration This retrospective multi-centric study included the 3591 frozen embryo transfers from 1st Apr 2022 to 31st Nov 2023 out of 4623 women who underwent oocyte retrieval from 1st Jan 2022. Patients were divided into study (group A) and control (group B). In group A, 1035 women received the transfers from spent culture media; in group B, 2556 women received transfers after shifting the blastocysts to fresh culture media before loading into the ET catheter. Participants/materials, setting, methods All the transfers considered in this study were day-5 blastocysts, irrespective of their frozen state. Day-5 frozen-thawed were incubated short-time (∼1 hour) before the transfer. Whereas, the frozen embryos and morulas were cultured till day 5. In the study group, all cultures were conducted in 100ul of culture media under oil per embryo to maintain consistency amongst the group. The rest of the laboratory and clinical procedures were consistent between the two groups. Main results and the role of chance The cumulative pregnancy rate was significantly higher in group A than in group B (60.9% Vs 55.6%; OR = 1.23; 95% CI, 1.07 -1.44, Z-score 2.901, P 0.003). The effect of spent culture media was further observed by regrouping the day-3 or 4 frozen (group A1) and day-5 frozen patients (group A2). Day-5 thawed blastocysts transferred after short incubation to allow the secretions to directly deposit on the endometrium. Group A1 might have a high concentration of secretions due to its accumulation from the embryo or morula stages. Pregnancy rates in group A1 were higher than A2 but not statistically significant (61.7% Vs 59.7%; OR = 1.08, 95% CI, 0.84-1.4, Z-score 0.654, P = 0.51). The less impact indicates that the feedback came from blastocysts rather than embryos. Limitations, reasons for caution It is not evident how these secretions contribute to biofeedback. Quantification, identifying their time of release and recovery from the qualitative tests for their therapeutic use are the limitations. Nevertheless, spent media can be employed if found beneficial. Wider implications of the findings We have taken a large possible data set for control against the test group and took cumulative pregnancy rate as the primary outcome indicator to prove biofeedback from blastocysts can improve the clinical outcomes irrespective of the age and other factors of infertility. Trial registration number Not applicable
M Motukuri (Mon,) studied this question.