Conventional IVF rather than ICSI when only on oocyte is retrieved: time to overcome irrational fears

Abstract Study question Is the use of conventional-IVF (c-IVF) a viable option in single oocyte retrieved cycles? Summary answer The use of c-IVF on single oocyte seems to be a successful strategy in terms of laboratory performance indicators outlined in the Vienna Consensus. What is known already Intracytoplasmic Sperm Injection (ICSI) has greatly improved the chances of reproductive success in cases of male factor infertility, but it is often used without strong evidence, such as in cases of low numbers of retrieved oocytes, assuming it will avoid unexpected total fertilization failure (TFF). On these bases, several ART centers irrationally opt for ICSI when few oocytes are retrieved. This approach is due to the fear of facing TFF the following day. This situation is boosted when only one oocyte is available. Available studies on c-IVF in these circumstances are generally reassuring, but evidence is limited and inconclusive. Study design, size, duration This is a monocentric retrospective observational study performed at the Infertility Unit of the Fondazione Ca' Granda Ospedale Maggiore Policlinico between 2014 and 2021. The primary outcome of the study is normal fertilization rate, which is expected to be ≥ 60% according to the Vienna Consensus. The study sample (about 300 cycles) was calculated to obtain a 95% CI within the range of ± 5%. A binomial distribution model was used to determine the 95%CI of proportions. Participants/materials, setting, methods Only women who had recovered one oocyte at the oocyte retrieval were included in the study. Collected data included age of both partners, previous pregnancies, female BMI, antral follicle count, total motile sperm count. A multivariate analysis was performed to identify predictive factors for fertilization. Based on the policy of our Center, c-IVF was performed only in case of normal sperm variables according to WHO 2010 manual and in the absence of history of TFF. Main results and the role of chance Out of 700 cycles with single oocyte retrievals, 304 were treated with c-IVF, which resulted in normal fertilization (2PN) in 209 cases, corresponding to a fertilization rate of 69% (95%CI: 63-74%). In 13 cycles, oocytes were shown to be immature (germinal vesicle or metaphase I) at the time of fertilization check. In these cases, fertilization could not occur. If we exclude them, the fertilization rate raised to 72% (209/291) (95%CI: 66-77%). This fertilization rate was within the Vienna Consensus KPI for competency range and was no more than 5% lower compared to the benchmark value. Clinical pregnancy and live birth rates per cycle were 14% and 11%, respectively. Finally, we compared baseline characteristics of cycles with normal fertilization to those with failed fertilization. Both univariate and multivariate analyses failed to identify predictive factors of fertilization. Limitations, reasons for caution The retrospective nature and the absence of a control group do not allow us to draw robust and definitive conclusions. However, the large sample sized allowed us a precise estimation of the fertilization rate. Wider implications of the findings Fear about TFF is not a valid reason to opt for ICSI in women retrieving only one oocyte. The use of ICSI increases costs without providing benefits. We also failed di identify predictive factors of fertilization, hampering the possibility to select a subgroup of women who may benefit from ICSI. Trial registration number Not applicable