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Purpose: During fertilisation, female and male pronuclei (PNs) migrate to the centre of the ooplasm, juxtapose, and break down synchronously in preparation for the first mitosis. While PN non-juxtaposition and PN breakdown (PNBD) asynchrony are occasionally observed, their developmental implications remain uncertain. This study investigated the possible relationships among the two phenomena, preimplantation development patterns, and live birth rates in single blastocyst transfers., Methods: A total of 1455 fertilised oocytes cultured in a time-lapse incubator were retrospectively analysed. Fertilised oocytes were divided into four groups according to the presence of PN juxtaposition and breakdown synchrony. The relationships of abnormal PN behaviour with embryo morphokinetics, blastocyst formation, and live birth were evaluated., Results: PN non-juxtaposition and asynchrony were observed in 1.9% and 1.0% of fertilised oocytes, respectively. The blastocyst cryopreservation rates in the synchronous-non-juxtaposed and asynchronous-non-juxtaposed groups were significantly lower than that in the synchronous-juxtaposed group. The rates of clinical pregnancy, ongoing pregnancy, and live birth were comparable among the groups. Non-juxtaposition was significantly associated with increased trichotomous cleavage at the first cytokinesis (P < 0.0001) and an increase in the time interval from PNBD to first cleavage (P < 0.0001). Furthermore, asynchronous PNBD was significantly correlated with increased rapid cleavage at the first cytokinesis (P = 0.0100)., Conclusion: Non-juxtaposition and asynchronous PNBD is associated with abnormal mitosis at the first cleavage and impaired preimplantation development. However, embryos displaying abnormal PNBD may develop to blastocyst stage and produce live births, suggesting blastocyst transfer as a more appropriate culture strategy., (© 2021. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Purpose: To determine age-adjusted overall success rates for patients undergoing clomiphene citrate only minimal stimulation cycle (mini) in vitro fertilization (IVF) without any gonadotropin administration., Methods: Eight hundred thirty-nine women (mean age: 38.4 ± 0.1 years; 2488 cycles) underwent clomiphene citrate only mini-IVF. Their first oocyte retrieval was between January 2009 and December 2009, with follow-up until December 2014. The cumulative live birth rate (CLBR) per oocyte retrieval cycle started and live birth rate per oocyte was retrospectively analyzed. The basic CLBR was calculated as the number of women who achieved a live birth divided by the total number of women who started oocyte retrieval., Results: The mean number of oocytes retrieved was 1.5. The basic CLBRs for all ages after the first and third cycles were 22.6% and 39.2%, respectively. For ≤ 34 years, 35-37 years, 38-40 years, 41-42 years, and ≥ 43 years, CLBRs after the first and third cycles were 42.5% and 70.1%, 32.9% and 49.1%, 20.0% and 38.6%, 12.6% and 25.2%, and 4.4% and 8.8%, respectively. These rates had a significant relationship with age (P < 0.01). The LBR per oocyte for all ages was 9.6%., Conclusion: Acceptable overall IVF success rates can be achieved in clomiphene citrate only mini-IVF, as well as acceptable LBR. The CLBRs and LBRs per oocyte are evidently influenced by women's age.