The application in IVF practice of modern techniques can improve positive outcome of each cycle in the assisted reproductive technology (ART) programs and the effectiveness of treatment as a whole. There are embryos in the female reproductive tract in physiological medium which contain various cytokines and growth factors. It plays an important role in the regulation of normal embryonic development, improve implantation and subsequently optimizing the development of the fetus and the placenta. Granulocyte macrophage colony-stimulating factor (GM-CSF is one of the cytokines playing an important role in reproductive function. Addition of recombinant GM-CSF to the culture medium can makes closer human embryos culture to in vivo conditions and improve the efficacy ART cycles. The analysis of culture embryos in EmbryoGen medium has shown that fertilization rate embryo culture and transfer to patients with previous unsuccessful attempts increases clinical pregnancy rate compared to the control group 39.1 versus 27.8%, respectively. It is noted that the implantation rate (on 7 weeks' gestation) and progressive clinical pregnancy rate (on 12 weeks' gestation) were significantly higher in group embryos culture in EmbryoGen medium compared to standard combination of medium (ISM1+VA), and were 20.4 and 17.4% versus 11.6 and 9.1%, respectively.

Currentliterature review presents the analysis of results of studies of morphological qualities and anomalies (dysmorphisms) of human oocytes in the field of assisted reproductive technologies. The variety of intracytoplasmic anomalies encountered in the clinical practice of in vitro fertilization, their effect on fertilization, cleavage, implantation frequency, clinical pregnancy rate were described. Moreover, the morphological characteristics of oocyte could be considered to use as biomarkers in predicting the quality of embryos and blastocysts, and further implantation potential.

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Study question Is there a difference in ART cycle results after frozen embryo transfer (FET), depending on whether blastocysts were cryopreserved on day 5 or 6? Summary answer There’s no statistical difference in the clinical pregnancy rate (CPR), life birth rate (LBR), miscarriage rate (MR) between embryos frozen on day 5 and 6. What is known already Currently, opinions differ regarding this topic. Previous studies demonstrated no difference in ongoing pregnancy rates between embryos frozen on day 5 (group A) or day 6 (group B) after FET. However, metanalysis (2019) suggested higher CPR and LBR after transferring embryos from group A rather than group B. It has also been established that ovarian stimulation leads to endometrial changes that result in deleterious effects on the implantation window and endometrial receptivity. Consequently, fresh transfers were excluded. Due to hormonal priming of endometrial receptivity, the same pregnancy outcomes should be expected with frozen-thawed blastocysts (day 5 vs 6). Study design, size, duration Retrospective cohort study was conducted between January 2015 and December 2018 with selected group of patients under 40 years of age. Group A consisted of 2275 cryotransfers of blastocyst expanded on day 5; group B included 170 cryotransfers of blastocyst on day 6. Both groups had an average of 1,52 embryos transferred per patient. Participants/materials, setting, methods Embryos were vitrified and warmed with Cryotop method (Kitazato, BioPharma). Blastocysts were scored according to Gardner and Schoolcraft grading system. Only expanded on day or 6 blastocysts of excellent and good (AA, AB, BA, BB) quality were selected. The embryos were cultured in CSC medium (Irvine Scientific) for 2–4 hours prior intrauterine transfer. The cycles with donor gametes, surrogacy and preimplantation genetic testing (PGT) were excluded. Statistical validity was assessed by Pearson’s chi-squared test. Main results and the role of chance The rates of the CPR, the ongoing pregnancy rate (OPR) and the LBR between group A and B were 50,8% (1157/2275) vs 46,5% (79/170) (p = 0,26), 37,4% (852/2275) vs 37,0% (63/170) (p = 0,91), 36,5% (832/2275) vs 35,2% (60/170) (p = 0,73) respectively and no significant differences were found in each category. Moreover, similarly there were no significant differences in the miscarriage rate 26,0% (301/1157) and 21,5% (17/79) (p = 0,37) as well Limitations, reasons for caution The study is limited due to uneven distribution of patients in both groups and by a low number of participants. The grading of blastocysts’ quality is also subjected to a human factor. Wider implications of the findings: This study confirms that frozen-thawed blastocysts do not seem to exhibit a difference in the CPR, OPR, LBR and MR whether they were expanded on day 5 or day 6. The cryopreservation of day 6 blastocyst can increase the chances of the patient for the positive outcome. Trial registration number Not applicable

Study question How does embryo transfer with a low-level of mosaicism affect the success of ART programs, pregnancy, and live birth in comparison with euploid embryo transfer? Summary answer The transfer of mosaic embryos results in the delivery of a healthy baby however significantly decreases the outcome of ART programs and live birth rate. What is known already Present methods of preimplantation genetic testing of aneuploidy (PGT-A) allow detecting a mixture of euploid and aneuploid cells at the blastocyst stage with high accuracy. Such embryos are classified as mosaics with varying levels according to the guidelines of the International Society for Preimplantation Genetic Diagnosis (PGDIS). Numerous sources describe that number of mosaic embryos can vary from 4 to 22%. Several publications report that mosaic embryos can lead to successful pregnancies and healthy childbirth, but with a lower frequency and higher rates of pregnancy loss compared to euploid embryos. Nevertheless, the effect of mosaicism on ART outcomes remains controversial. Study design, size, duration It has been analyzed 2506 embryos from 648 patients undergoing the ART program with PGT-A at the Institute of Reproductive Medicine for 2018 - 2019. Embryos after PGT-A were classified as euploid, aneuploid, and having mosaicism of less than 40% as low level and more than 40% as high level following PGDIS guidelines. Patients of (group A) were transferred 467 single euploid embryos, and 43 patients (group B) underwent single low-level mosaic embryo transfer. Participants/materials, setting, methods The embryos on day 5 or 6 were graded by Gardner Scoring System. Approximately 5–10 TE cells were biopsied from good quality blastocysts and subsequently vitrified. PGT-A was performed utilizing an array comparative genomic hybridization (aCGH) (Agilent). The transfer of mosaic embryos was performed in the absence of an alternative, only after medical genetic counseling with a risk explanation and the subsequent signing of an informed agreement. Statistical tests processed by Pearson’s chi-squared test. Main results and the role of chance Of all analyzed embryos, the proportion of euploid embryos was 48.6% (n = 1002), the total number of mosaics was 18.6% (n = 384) and aneuploid ones were 32.8% (n = 676). Depending on the level of mosaicism, the ratio between embryos with low-level mosaicism (≤40%) / high-level (≥40%) was 38.3% / 61.7%, respectively. According to the study, there was a significant decrease in the indicator of clinical pregnancy rate after embryo transfer with a low-level of mosaicism of 44.1% versus 63.2% transferred euploid embryo (р<0,01), however, despite an increase losses pregnancy in the group B (26.3%) there was no significant difference (p = 0.16) in comparison with the control group (15.4%). The live birth rate (LBR) significantly decreased (p < 0.001) after the transfer of the mosaic embryo by 32.5%, while in the control group the indicator was 53.9%. In all cases, after the transfer of the mosaic embryo, healthy babies were born. There were 2 cases of high-level mosaic embryo transfer as a result of which pregnancy did not occur. According to the survey, about 70% of patients agree to replant mosaic embryos, 20% are ready to go to the new program, and 10% cannot make a decision. Limitations, reasons for caution The number of patients in group B was significantly lower than in group A. Not enough cases of embryo transfer with a high-level of mosaicism. Wider implications of the findings: The current study might help to develop and to select a more appropriate strategy for transfer mosaic embryos. The next series of studies should focus on obstetric and neonatal outcome data from mosaic embryo transfer to gain a better understanding of the chromosomal and physiological health of children. Trial registration number Not applicable