A standardized training allows achieving similar clinical pregnancy rates per top-quality euploid blastocyst transfer across operators.

Purpose To evaluate the performance of different embryo transfer (ET) operators in a strictly controlled scenario minimizing potential confounders.

This single-center retrospective cohort study analyzed vitrified-warmed single euploid top-quality day-5 blastocyst transfers performed in non-obese women at the same IVF center by four equally trained clinicians using a standardized ET technique. These strict inclusion criteria allowed excluding all main confounders on the primary study outcome, namely clinical pregnancy rate (CPR) per ET across different operators. Endometrial preparation protocol, maternal age at transfer, parity, and the embryologist involved were assessed as putative further confounders.

Out of 8663 ETs performed between January 2013 and December 2021, 421 first single euploid top-quality blastocyst transfers were included. No significant difference in ET outcomes was observed among clinicians. Multivariate logistic regression analysis confirmed no association between ET operators and CPR. The experience—defined as the sequential number of previous ETs conducted—did not involve any increase in the CPR.

The ET operator does not affect ET outcomes when subject to the same training and adopting a standardized ET protocol. As the performance does not increase with experience, the initial training is crucial to standardize the procedure across clinicians. In this regard, the CPR per euploid transfer can be considered a valuable Key Performance Indicator (KPI) for quality control purposes. Larger studies are required to build a consensus on competence and benchmark values to achieve. Similar content being viewed by others Data availability Data regarding any of the subjects in the study has not been previously published and will be made available to the editors of the journal for review or query upon request. The data underlying this article are available in the article and in its online Supplemental material.

Practice Committee of the American Society for Reproductive Medicine. Electronic address: [email protected], Penzias A, Bendikson K, Butts S, Coutifaris C, Falcone T, et al. ASRM standard embryo transfer protocol template: a committee opinion. Fertil Steril 2017;107:897–900. https://doi.org/10.1016/j.fertnstert.2017.02.108. Practice Committee of the American Society for Reproductive Medicine. Electronic address: [email protected], Practice Committee of the American Society for Reproductive Medicine. Performing the embryo transfer: a guideline. Fertil Steril 2017;107:882–96. https://doi.org/10.1016/j.fertnstert.2017.01.025. D’Angelo A, Panayotidis C, Alteri A, Mcheik S, Veleva Z. Evidence and consensus on technical aspects of embryo transfer. Hum Reprod Open 2022;2022:hoac038. https://doi.org/10.1093/hropen/hoac038. Tyler B, Walford H, Tamblyn J, Keay SD, Mavrelos D, Yasmin E, et al. Interventions to optimize embryo transfer in women undergoing assisted conception: a comprehensive systematic review and meta-analyses. Hum Reprod Update. 2022;28:480–500. https://doi.org/10.1093/humupd/dmac009. Karande VC, Morris R, Chapman C, Rinehart J, Gleicher N. Impact of the “physician factor” on pregnancy rates in a large assisted reproductive technology program: do too many cooks spoil the broth? Fertil Steril. 1999;71:1001–9. https://doi.org/10.1016/s0015-0282(99)00139-9. Hearns-Stokes RM, Miller BT, Scott L, Creuss D, Chakraborty PK, Segars JH. Pregnancy rates after embryo transfer depend on the provider at embryo transfer. Fertil Steril. 2000;74:80–6. https://doi.org/10.1016/s0015-0282(00)00582-3. Angelini A, Brusco GF, Barnocchi N, El-Danasouri I, Pacchiarotti A, Selman HA. Impact of physician performing embryo transfer on pregnancy rates in an assisted reproductive program. J Assist Reprod Genet. 2006;23:329–32. https://doi.org/10.1007/s10815-006-9032-6. Yao Z, Vansteelandt S, Van der Elst J, Coetsier T, Dhont M, De Sutter P. The efficacy of the embryo transfer catheter in IVF and ICSI is operator-dependent: a randomized clinical trial. Hum Reprod. 2009;24:880–7. https://doi.org/10.1093/humrep/den453. Cirillo F, Patrizio P, Baccini M, Morenghi E, Ronchetti C, Cafaro L, et al. The human factor: does the operator performing the embryo transfer significantly impact the cycle outcome? Hum Reprod. 2020;35:275–82. https://doi.org/10.1093/humrep/dez290. Cimadomo D, Rienzi L, Conforti A, Forman E, Canosa S, Innocenti F, et al. Opening the black box: why do euploid blastocysts fail to implant? A systematic review and meta-analysis. Hum Reprod Update. 2023;29:570–633. https://doi.org/10.1093/humupd/dmad010. ESHRE Clinic PI Working Group, Vlaisavljevic V, Apter S, Capalbo A, D’Angelo A, Gianaroli L, et al. The Maribor consensus: report of an expert meeting on the development of performance indicators for clinical practice in ART. Hum Reprod Open 2021;2021:hoab022. https://doi.org/10.1093/hropen/hoab022. Fabozzi G, Cimadomo D, Maggiulli R, Vaiarelli A, Ubaldi FM, Rienzi L. Which key performance indicators are most effective in evaluating and managing an in vitro fertilization laboratory? Fertil Steril. 2020;114:9–15. https://doi.org/10.1016/j.fertnstert.2020.04.054. Cimadomo D, Capalbo A, Dovere L, Tacconi L, Soscia D, Giancani A, et al. Leave the past behind: women’s reproductive history shows no association with blastocysts’ euploidy and limited association with live birth rates after euploid embryo transfers. Hum Reprod. 2021;36:929–40. https://doi.org/10.1093/humrep/deab014. Vaiarelli A, Cimadomo D, Patrizio P, Venturella R, Orlando G, Soscia D, et al. Biochemical pregnancy loss after frozen embryo transfer seems independent of embryo developmental stage and chromosomal status. Reprod Biomed Online. 2018;37:349–57. https://doi.org/10.1016/j.rbmo.2018.05.019. Maggiulli R, Cimadomo D, Fabozzi G, Papini L, Dovere L, Ubaldi FM, et al. The effect of ICSI-related procedural timings and operators on the outcome. Hum Reprod. 2020;35:32–43. https://doi.org/10.1093/humrep/dez234. Capalbo A, Rienzi L, Cimadomo D, Maggiulli R, Elliott T, Wright G, et al. Correlation between standard blastocyst morphology, euploidy and implantation: an observational study in two centers involving 956 screened blastocysts. Hum Reprod. 2014;29:1173–81. https://doi.org/10.1093/humrep/deu033. Cimadomo D, Scarica C, Maggiulli R, Orlando G, Soscia D, Albricci L, et al. Continuous embryo culture elicits higher blastulation but similar cumulative delivery rates than sequential: a large prospective study. J Assist Reprod Genet. 2018;35:1329–38. https://doi.org/10.1007/s10815-018-1195-4. Maggiulli R, Giancani A, Cimadomo D, Ubaldi FM, Rienzi L. Human blastocyst biopsy and vitrification. J Vis Exp. 2019. https://doi.org/10.3791/59625. Gardner D, Schoolcraft WB. In vitro culture of human blastocyst. In: Jansen R, Mortimer D, editors. Towards reproductive certainty: infertility and genetics beyond. Carnforth: Parthenon Press; 1999. p. 377–88. Cimadomo D, Soscia D, Casciani V, Innocenti F, Trio S, Chiappetta V, et al. How slow is too slow? A comprehensive portrait of day 7 blastocysts and their clinical value standardized through artificial intelligence. Hum Reprod. 2022;37:1134–47. https://doi.org/10.1093/humrep/deac080. ESHRE PGT Consortium Steering Committee, Carvalho F, Coonen E, Goossens V, Kokkali G, Rubio C, et al. ESHRE PGT Consortium good practice recommendations for the organisation of PGT. Hum Reprod Open 2020;2020:hoaa021. https://doi.org/10.1093/hropen/hoaa021. Capalbo A, Treff NR, Cimadomo D, Tao X, Upham K, Ubaldi FM, et al. Comparison of array comparative genomic hybridization and quantitative real-time PCR-based aneuploidy screening of blastocyst biopsies. Eur J Hum Genet. 2015;23:901–6. https://doi.org/10.1038/ejhg.2014.222. Capalbo A, Poli M, Rienzi L, Girardi L, Patassini C, Fabiani M, et al. Mosaic human preimplantation embryos and their developmental potential in a prospective, non-selection clinical trial. Am J Hum Genet. 2021;108:2238–47. https://doi.org/10.1016/j.ajhg.2021.11.002. Lewin A, Schenker JG, Avrech O, Shapira S, Safran A, Friedler S. The role of uterine straightening by passive bladder distension before embryo transfer in IVF cycles. J Assist Reprod Genet. 1997;14:32–4. https://doi.org/10.1007/BF02765749. McQueen DB, Robins JC, Yeh C, Zhang JX, Feinberg EC. Embryo transfer training in fellowship: national and institutional data. Fertil Steril. 2020;114:1006–13. https://doi.org/10.1016/j.fertnstert.2020.06.004. Miller CM, Weaver AL, Zhao Y, Babayev SN. Outcomes of embryo transfers performed by Reproductive Endocrinology and Infertility fellows vs. faculty: an 11-year retrospective review. Fertil Steril 2022;117:115–22. https://doi.org/10.1016/j.fertnstert.2021.08.044. Lu MC. Impact of “non-physician factors” on the “physician factor” of in vitro fertilization success: is it the broth, the cooks, or the statistics? Fertil Steril. 1999;71:998–1000. https://doi.org/10.1016/s0015-0282(99)00135-1. Cirillo F, Spadaro D, Morenghi E, Baccini M, Busnelli A, Ronchetti C, et al. Different actors for the same play: the impact of the embryologist performing the embryo transfer. Reprod Biomed Online. 2022;45:661–8. https://doi.org/10.1016/j.rbmo.2022.06.002. Glujovsky D, Quinteiro Retamar AM, Alvarez Sedo CR, Ciapponi A, Cornelisse S, Blake D. Cleavage-stage versus blastocyst-stage embryo transfer in assisted reproductive technology. Cochrane Database Syst Rev 2022;5:CD002118. https://doi.org/10.1002/14651858.CD002118.pub6. Ferreux L, Bourdon M, Sallem A, Santulli P, Barraud-Lange V, Le Foll N, et al. Live birth rate following frozen-thawed blastocyst transfer is higher with blastocysts expanded on day 5 than on day 6. Hum Reprod. 2018;33:390–8. https://doi.org/10.1093/humrep/dey004. ESHRE Guideline Group on the Number of Embryos to Transfer, Alteri A, Arroyo G, Baccino G, Craciunas L, De Geyter C, et al. ESHRE guideline: number of embryos to transfer during IVF/ICSI†. Hum Reprod 2024;39:647–57. https://doi.org/10.1093/humrep/deae010. Practice Committee of the American Society for Reproductive Medicine and the Practice Committee for the Society for Assisted Reproductive Technologies. Electronic address: [email protected]. Guidance on the limits to the number of embryos to transfer: a committee opinion. Fertil Steril 2021;116:651–4. https://doi.org/10.1016/j.fertnstert.2021.06.050. Papageorgiou TC, Hearns-Stokes RM, Leondires MP, Miller BT, Chakraborty P, Cruess D, et al. Training of providers in embryo transfer: what is the minimum number of transfers required for proficiency? Hum Reprod. 2001;16:1415–9. https://doi.org/10.1093/humrep/16.7.1415. Phillips JAS, Martins WP, Nastri CO, Raine-Fenning NJ. Difficult embryo transfers or blood on catheter and assisted reproductive outcomes: a systematic review and meta-analysis. Eur J Obstet Gynecol Reprod Biol. 2013;168:121–8. https://doi.org/10.1016/j.ejogrb.2012.12.030. Zhang HX, Li F, Jin H, Song WY, Su Y, Li G. Effect of retained embryos on pregnancy outcomes of in vitro fertilization: a matched retrospective cohort study. BMC Pregnancy Childbirth. 2023;23:5. https://doi.org/10.1186/s12884-022-05315-5. Kadour-Peero E, Tulandi T, Feferkorn I, Hiszkiahu R, Buckett W. Effects of embryo retention during embryo transfer on IVF outcomes. J Assist Reprod Genet. 2022;39:1065–8. https://doi.org/10.1007/s10815-022-02450-y. Kava-Braverman A, Martínez F, Rodríguez I, Álvarez M, Barri PN, Coroleu B. What is a difficult transfer? Analysis of 7,714 embryo transfers: the impact of maneuvers during embryo transfers on pregnancy rate and a proposal of objective assessment. Fertil Steril. 2017;107:657-663.e1. https://doi.org/10.1016/j.fertnstert.2016.11.020. Galati G, Reschini M, Mensi L, Di Dio C, Somigliana E, Muzii L. The impact of difficult embryo transfer on the success of IVF: a systematic review and meta-analysis. Sci Rep. 2023;13:22188. https://doi.org/10.1038/s41598-023-49141-x. Levi Setti PE, Cirillo F, Morenghi E, Immediata V, Caccavari V, Baggiani A, et al. One step further: randomised single-centre trial comparing the direct and afterload techniques of embryo transfer. Hum Reprod. 2021;36:2484–92. https://doi.org/10.1093/humrep/deab178. Cirillo F, Immediata V, Ronchetti C, Carletti T, Morenghi E, Albani E, et al. Steps forward in embryo transfer technique: a retrospective study comparing direct versus afterload catheters at different time frames. J Assist Reprod Genet. 2023;40:2895–902. https://doi.org/10.1007/s10815-023-02957-y. McQueen DB, Borazjani A, Yeh C, Dong S, Milad MP, Feinberg EC. The use of an embryo transfer simulator to compare transfer techniques and pregnancy outcomes among physicians. F S Rep. 2024;5:183–8. https://doi.org/10.1016/j.xfre.2024.04.003. Author information Authors and Affiliations Contributions A.R., D.C., and A.V. were involved in the study design, data analysis, and manuscript preparation. D.C. was involved in the statistical analysis. E.P., F.I., M.T., S.C., M.G., D.M.S., G.C., V.C., L.A., and G.F. collected the data and contributed to the discussion. F.M.U. and L.R. were involved in study implementation and supervision, expert knowledge, and manuscript revision. All authors read and approved the manuscript. Corresponding author Ethics declarations Ethics approval Ethic committee approval was obtained for the retrospective analysis of pseudonymized data aimed at identifying patients’, cycles’, or embryos’ features associated with IVF efficacy and/or efficiency. Competing interests The authors declare no competing interests. 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J Assist Reprod Genet 42, 875–884 (2025). https://doi.org/10.1007/s10815-025-03396-7 Received: Accepted: Published: Version of record: Issue date: DOI: https://doi.org/10.1007/s10815-025-03396-7