In 192 oocyte donation cycles performed between January 1993 and July 1996, we examined the width of 'the window for embryo transfer' using standard hormonal replacement methods. All transfers were performed within 48 h of insemination. We varied the day of embryo transfer with regard to the initiation of progesterone therapy and, thus, the duration of endometrial exposure to progesterone and analysed the resulting pregnancy rates. Patients were divided into five groups (I-V) and embryo transfers were performed 2, 3, 4, 5 or 6 days following initiation of progesterone therapy. The number of pregnancies per transfer cycle achieved in groups I-V were 0 (0%), 3 (12%), 16 (40%), 29 (48.3%), and 10 (20.4%) respectively. The increased pregnancy rate in group III in comparison to group II is statistically significant (P < 0.03). Furthermore, the pregnancy rate in group IV (5 days of progesterone administration before embryo transfer) was significantly higher than in group V (6 days of progesterone administration before embryo transfer; P < 0.005). We also noted that, when embryos were transferred 4 or 5 days after initiation of progesterone therapy, the pregnancy rates were not significantly different between menopausal and cycling recipients (50% vs 43.7%). Our results indicate that the window for embryo transfer is dependent on duration of treatment with progesterone; it begins approximately 48 h after starting progesterone administration and lasts for approximately 4 days. The optimum period for transferring embryos at the 4- to 8-cell stage corresponds to cycle days 18 and 19. Transfers performed on the 17th and 20th days of the cycle can result in successful implantation, although the rates of implantation are highest when transfers are done on days 18 and 19.

Males with abnormal karyotypes and subgroups of fertile and infertile males with normal karyotypes may be at risk of producing unbalanced or aneuploid spermatozoa. Biological, clinical, environmental and other factors may also cause additional sperm aneuploidy. However, increased risk of sperm aneuploidy is directly related to chromosomally abnormal embryo production and hence to poor reproductive potential. This systemic literature review focuses on the identification of these males because this is an essential step in the context of assisted reproduction. This research may allow for a more personalised and, hence, more accurate estimation of the risk involved in each case, which in turn will aid genetic counselling for affected couples and help with informed decision-making.

Microinjection of spermatids into oocytes has proven to be a successful assisted reproduction procedure in the animal model. In the human, low fertilization and cleavage to the 4-cell stage were reported after intracytoplasmic sperm injection (ICSI) with round spermatids. In comparison with a conventional ICSI-testicular sperm extraction (TESE) programme, the implantation rate after round spermatid injection is dramatically low. Different problems have been encountered during the development of the spermatid injection technique and they could be partially responsible for the lower outcome when using round spermatids. Compared with the round spermatid cells, spermatids in the elongation phase are easy to isolate and identify from other round cells present in a wet preparation. The morphological identification does not reveal anything about the viability or the genetic normality of the round spermatids. Severe testicular dysfunction may have consequences on the quality of the few spermatogenic cells present. Others factors, such as the pathology of the patient, play an important role in the successful treatment. Even if the results are extremely low, spermatid injection seems more favourable for men who have already proven their capacity to produce some spermatozoa. A spermatogenic block at the round spermatid level has led to early abortions, increasing the suspicion of the role of a genetic factor. In order for this technique to be safe for use in clinics, more intensive work is needed to improve the selection and handling of cells and to ascertain the genomic imprinting and gene expression necessary for embryonic development. Hence, when using immature cells for conception, the screening of the patient and the follow-up of the pregnancies and babies should be mandatory.

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Study question Is multinucleation during cleavage stage correlated with the ploidy status of embryos and how does it affect the clinical outcome? Summary answer The presence of multinucleated embryos does not affect clinical outcome, although the risk of aneuploidy is higher in multinucleated embryos. What is known already Multinucleated blastomeres (ΜΝ) of cleavage stage embryos has been reported widely in scientific literature. Multinucleation has been associated with diminished embryo developmental competency and clinical outcomes such as lower implantation. Although this is an intriguing subject of research, it is not clear yet whether multinucleation is related to aneuploidy. Morphological irregularities such as multinucleation in blastomeres became a constant finding only after the perpetually evolving technology of time-lapse culture of embryos which in combination with PGT-A analysis, creates new research paths which aim to develop a new tool for selection or deselection of embryos for transfer. Study design, size, duration This retrospective study, included 97 PGT-A cycles, performed at Embryolab fertility clinic from May 2017 to December 2020, all cultured in time-lapse incubator (EmbryoScope). Two study groups were formed; the MN Group consisted of PGT-A cycles with at least one multinucleated embryo (n = 56) and the Control Group in which all PGT-A cycles had no multinucleated embryos (n = 38). Euploidy rate, type of chromosomal abnormality, cumulative pregnancy and live birth rates were compared between the two groups. Participants/materials, setting, methods Embryos were annotated for the existence of multinucleated blastomeres on Day 2 of their development. Biopsy was performed on Days 5/6 and embryos were genetically tested. One or two euploid embryos were transferred. Euploidy rate and clinical outcomes between the two groups were compared. Within the MN group, euploidy rate between multinucleated and non-multinucleated embryos was compared. For abnormal embryos, association of multinucleation with the type of abnormality was tested. SAS statistical analysis was performed. Main results and the role of chance Mean female age was 35.93 years in the MN group and 38.39 years in the control group. Blastocyst formation rate (expressed per fertilised oocytes) was similar between MN and Control group (74% vs 76%, p = 0.6303). In the MN group, 56 cases resulted in 44 embryo transfers while in the control group 38 cases resulted in 23 embryo transfers. Pregnancy rates (59.09% vs 65.21%, p = 0.6255) and clinical pregnancy rates (45.45% vs 39.13%, p = 0.4245) were not significantly different between MN and Control group. Initially, cumulative live birth rate was found to be significantly higher in the MN group compared to the Control group (62.96% vs 33.34%, p = 0.0417). However, when logistic and poisson regression was applied, it became obvious that this difference was not affected by multinucleation but from other factors such as female age. When comparing multinucleated and non-multinucleated embryos within the MN group, it was found that the mean number of euploid embryos was significantly higher in the non-multinucleated subgroup of embryos (p = 0.0021). No correlation was found between multinucleation and the type of chromosomal abnormality. Limitations, reasons for caution The sample size is the main limitation of the present study. More research with bigger sample size is needed in order to confirm the finding of the present study. Wider implications of the findings: The present study suggests that multinucleated blastomeres during embryo development is not an indication for diminished blastocyst formation and does not affect the clinical outcomes. However, within a sibling embryo population, non-multinucleated embryos tend to be euploid and this finding can be used to advance embryo selection efficiency. Trial registration number Not applicable