RESUMO
STUDY QUESTION: What is the impact of day after rescue ICSI (r-ICSI) on success of fresh and frozen embryo transfers? SUMMARY ANSWER: The use of r-ICSI can virtually allay fears of total fertilization failure (TFF) after conventional IVF (C-IVF) and achieve high live birth rates after frozen blastocyst transfer. WHAT IS KNOWN ALREADY: More infertility clinics have resorted to the use of ICSI in place of C-IVF in IVF treatment owing to fear of TFF or a low fertilization rate. r-ICSI has been attempted either on the day of IVF or the day after. Day after r-ICSI has proved unsuccessful in the past. STUDY DESIGN, SIZE, DURATION: A retrospective data analysis was performed of 16 608 qualifying cases between April 2010 and July 2021 conducted at a single private academically affiliated fertility clinic. PARTICIPANTS/MATERIALS, SETTING, METHODS: r-ICSI was performed principally on patients with >4 metaphase II oocytes, showing no signs of fertilization 18 h after C-IVF. C-IVF was performed on patients who had >4 million total motile sperm after preparation. r-ICSI was then performed 18-24 h after insemination, using the sperm sample from the previous day. r-ICSI fertilization rates, cryopreservation of cleavage and blastocysts embryos, and pregnancy rates after fresh or frozen transfer were then assessed. MAIN RESULTS AND THE ROLE OF CHANCE: r-ICSI was performed on 377 patients (2.3% of eligible retrieval cycles) who had a mean (±SD) female and male age of 35.9 ± 4.5 and 38.1 ± 9.1 years, respectively. A total of 5459 oocytes were initially retrieved. Of the oocytes undergoing r-ICSI, 2389 (49.5%) fertilized normally, and 205 (54.4%) patients underwent a fresh embryo transfer. The live birth rates were 23/186 (12.3%) for fresh cleavage and 5/19 (26.3%) for fresh blastocyst stage transfers. In 145 cycles a blastocyst was frozen, and 137 transfers were performed with a 64/137 (46.7%) live birth rate. Of the 377 cycles receiving r-ICSI only, 25 of the qualifying cases failed to have any fertilization, reducing TFF to 25/16 608 (0.15%). LIMITATIONS, REASONS FOR CAUTION: This was a single-center retrospective study on a specific subset of patients, which may limit its generalizability to other clinics. WIDER IMPLICATIONS OF THE FINDINGS: r-ICSI allows a second opportunity to fertilize oocytes despite poor initial outcomes. Patients who had a frozen blastocyst transfer achieved high live birth rates, indicating that a resynchronization of the embryo with the endometrium can optimize r-ICSI cases. r-ICSI allays fears of TFF when using C-IVF, providing evidence that the overuse of ICSI in patients without male factor may not be warranted. STUDY FUNDING/COMPETING INTEREST(S): The study was internally funded by Boston IVF. The authors declare that they have no conflict of interest in relation to the data published in the article. TRIAL REGISTRATION NUMBER: N/A.