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At present, the success of non-surgical embryo recovery (NSER) and transfer (NSET) hinges upon the cervical passage of catheters, but penetration of the uterine cervix in ewes is problematic due to its anatomical structure (i.e., long and narrow cervical lumen with misaligned folds and rings). It is a major obstacle limiting the widespread application of NSER and NSET in sheep. While initial attempts to traverse the uterine cervix focused on adapting or re-designing insemination catheters, more recent studies demonstrated that cervical relaxation protocols were instrumental for transcervical penetration in the ewe. An application of such protocols more than tripled cervical penetration rates (currently at 90-95 %) in sheep of different breeds (e.g., Dorper, Lacaune, Santa Inês, crossbred, and indigenous Brazilian breeds) and ages/parity. There is now sufficient evidence to suggest that even repeatedly performed cervical passages do not adversely affect overall health and reproductive function of ewes. Despite these improvements, appropriate selection of donors and recipients remains one of the most important requirements for maintaining high success rates of NSER and NSET, respectively. Non-surgical ovine embryo recovery has gradually become a commercially viable method as even though the procedure still cannot be performed by untrained individuals, it is inexpensive, yields satisfactory results, and complies with current public expectations of animal welfare standards. This article reviews critical morphophysiological aspects of transcervical embryo flushing and transfer, and the prospect of both techniques to replace surgical methods for multiple ovulation and embryo transfer (MOET) programs in sheep. We have also discussed some potential pharmacological and technical developments in the field of non-invasive embryo recovery and deposition.

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Microinjection of CRISPR/Cas9 requires the availability of zygotes that implies animal breeding, superovulation schemes, and embryo collection. Vitrification of zygotes may allow having ready-to-use embryos and to temporally dissociate the workload of embryo production from microinjection. In this study, fresh (F group) or vitrified (V group) zygotes were microinjected with CRISPR/Cas9 system to test the hypothesis that vitrified zygotes could be a suitable source of embryos for microinjection. In Experiment 1 (in vitro evaluation), B6D2F1/J zygotes were microinjected and cultured until blastocyst stage. Embryo survival and cleavage rates after microinjection were similar between groups (~50% and ~80% respectively; P = NS). Development rate was significantly higher for F than V group (55.0% vs. 32.6%, respectively; P<0.05). Mutation rate did not show statistical differences among groups (P = NS). In Experiment 2 (in vivo evaluation), C57BL/6J zygotes were microinjected and transferred to recipient females. Embryo survival was significantly lower in fresh than in vitrified zygotes (49.2% vs. 62.7%, respectively; P<0.05). Cleavage rate did not show statistical differences (~70%; P = NS). Pregnancy rate (70.0% vs. 58.3%) and birth rate (11.9% vs. 11.2%) were not different between groups (F vs. V group; P = NS). Offspring mutation rate was higher for F than V group, in both heterodimer analysis (73.7% vs. 33.3%, respectively; P = 0.015) and Sanger sequencing (89.5% vs. 41.7%, respectively; P = 0.006). In conclusion, vitrified-warmed zygotes present a viable alternative source for CRISPR/Cas9 microinjection when the production of fresh embryos is impeded by limited technical support. The possibility of zygote cryobanking to perform microinjection sessions on demand seems to be a suitable alternative to avoid the breeding and maintenance of animals all over the year, enhancing the implementation of CRISPR technology.

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OBJECTIVE: The safety of assisted reproductive technology can be assessed by examining birth weight as an outcome measure. The objective of this study was to evaluate the effect of endometrial thickness during embryo transfer on newborn birth weight and preterm labor. METHODS: We conducted a retrospective cohort study at the infertility department of a teaching hospital affiliated with a university of medical sciences. Eligible women were ≥18 years old and conceived a singleton pregnancy with embryo transfer and an endometrial thickness of ≥7 mm. None of the patients had diabetes, blood hypertension, and polycystic ovarian syndrome. We assessed maternal and newborn characteristics and perinatal pregnancy outcomes. RESULTS: In total, 100 eligible patients with a mean (SD) age of 32.8 (6.2) years were included. The mean endometrial thickness during embryo transfer was 9.1 (1.2) mm, and the mean birth weight was 3040.7 (565.3)g. There were no statistically significant associations between endometrial thickness and preterm labor (p=0.215) and between endometrial thickness and stillbirth or intra-uterine fetal death (p=0.880). However, after adjusting for confounding factors, the association of endometrial thickness with birth weight was statistically significant [b=124.6 (51.6), p=0.018]. CONCLUSIONS: Within the range of ≥7mm, endometrial thickness during embryo transfer is a predictor of newborn weight; however, it is not related to the risk of preterm labor, stillbirth, or intra-uterine fetal death.

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OBJECTIVE: The aim of this study was to compare endometrial thickness with the use of transdermal estrogen (gel) versus oral estrogen (pills) for endometrial preparation in the frozen embryo transfer cycle and serum estrogen concentrations during the preparation cycle, side effects, and chemical and clinical pregnancy rates. METHODS: This was a prospective, randomized controlled trial of women undergoing endometrial preparation for cryopreserved blastocyst transfer. A total of 88 women were randomized, of which 82 completed the study protocol. Of this group, 44 received 6 mg/day of estradiol valerate orally (pills group) and 38 received 4.5 mg/day of estradiol hemihydrate transdermally (gel group). Endometrial thickness was measured using transvaginal ultrasound between the 7 and 10th day of the cycle. Serum estradiol concentrations were measured on the day of initiating the cycle, on control transvaginal ultrasounds, and on the day of embryo transfer. Side effects were documented at each study visit. p<0.05 were adopted as statistically significant. The groups were compared using Student's t-test for continuous variables and chi-square or Fisher's exact test for categorical variables. RESULTS: There were no significant group differences (p>0.05) in endometrial thickness, biochemical and clinical pregnancy rates, miscarriage rate, blood estradiol concentrations, duration of estradiol administration, or cycle cancellation rates. CONCLUSION: Endometrial preparation with transdermal estrogen yielded similar reproductive outcomes to oral estrogen with fewer side effects.

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OBJECTIVE: To evaluate the impact of double embryo vitrification on clinical outcomes. METHODS: This retrospective cohort study included data from January 2013 to March 2021. The study group included women aged 33.3±5.7 years with double-vitrified embryos (n=381), while the control group included women aged 32.1±6.7 years with embryos vitrified once (n=780), all transferred at the blastocyst stage. The primary endpoint was live birth rate (LBR), and secondary endpoints included percent positive ßHCG test, clinical/ongoing pregnancy rates, miscarriage/biochemical pregnancy rates and birthweight. RESULTS: LBR was significantly lower in double-vitrified embryos (30.2%) than in embryos vitrified once (45.6%, p<.05). Similarly, double-vitrified embryos were associated with significantly lower positive ßHCG tests (46% vs. 63.3%, p<.05) and clinical (34.9% vs. 52.2%, p<.05) and ongoing pregnancy (31.3% vs. 47.3%, p<.05) rates compared to embryos vitrified once. However, biochemical pregnancy (double vitrified: 24.1% vs. vitrified once: 17.9%, p>.05) and miscarriage rates (double vitrified: 10.2% vs. vitrified once: 9.4%, p>.05), as well as mean birthweight (double-vitrified embryos: 2950g vs. embryos vitrified once: 2837g, p>.05) did not differ significantly between two groups. On a secondary comparison, amongst double-vitrified embryos, the subgroup that was cultured for more than 24 hours between warming and second vitrification achieved significantly higher positive ßHCG tests (49%) and clinical pregnancy (38%) rates, compared to embryos re-vitrified on the same day of warming (31.8% and 20.5%, respectively, p<.05). Nevertheless, LBR did not differ significantly amongst these study-group embryos (embryos that remained in culture for more than 24 hours: 32.2% vs. embryos that were re-vitrified on warming day: 20.5%, p>.05). CONCLUSIONS: Double vitrification of embryos adversely affects clinical outcomes. However, it represents a valuable option concerning embryo wastage, with acceptable success rates.

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OBJECTIVE: Recently, it has been discussed whether or not mosaic embryo transfers should be performed since they might result in viable pregnancies, although they often end up being discarded. We report a case of successful pregnancy, after a mosaic embryo transfer from an in vitro matured egg and frozen PESA sperm. CASE DESCRIPTION: Tests performed on a female aged 40 years and a male aged 37 years seeking fertility treatment found she had an adequate ovarian reserve and patent fallopian tubes. He had a history of cryptorchidism and inguinal hernia repair. The spermogram showed azoospermia, and testicular ultrasound showed an atrophic left testicle and a normal right testis. The vas deferens was palpated during physical examination. Intracytoplasmic sperm injection with percutaneous epididymal sperm aspiration (PESA) was indicated. Two cycles of IVF after controlled ovarian stimulation with follitropin delta was performed. In the first cycle, seven mature eggs were inseminated, two fertilized normally, resulting in one blastocyst biopsied and analyzed by NGS with complex aneuploid results. In the second cycle, frozen sperm from PESA was used. Three eggs were inseminated on the day of the procedure (resulting in 2 blastocysts), and three in vitro matured eggs were inseminated after 24 hours (resulting in 1 blastocyst). NGS analysis showed two complex aneuploid embryos and one 40% low-level trisomy 20 aneuploid mosaicism (+20) for the post 24-hour embryo. A mosaic embryo transfer was performed, resulting in clinical pregnancy and birth of a healthy baby girl with a normal blood karyotype. DISCUSSION: Mosaic embryo transfer is a topic for discussion. Certain levels of mosaicism do not seem to pose risks to the development of the fetus.

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STUDY QUESTION: Does a personalized embryo transfer (pET) guided by tests for endometrial receptivity (TER) increase the effectiveness of ART procedures? SUMMARY ANSWER: The use of TER-guided pET is not supported by current published evidence in women without repeated implantation failure (RIF), while in women with RIF more research is needed to assess a potential benefit. WHAT IS KNOWN ALREADY: Implantation rates are still far from ideal, especially in some patients that have RIF with good-quality embryos. As a potential solution, a wide range of diverse TER use different sets of genes to identify displacements of the window of implantation to adjust the individual length of progesterone exposure in a pET. STUDY DESIGN, SIZE, DURATION: A systematic review with meta-analysis was performed. Search terms included endometrial receptivity analysis, ERA, personalized embryo transfer. CENTRAL, PubMed, Embase, reference lists, clinical trials registers, and conference proceedings (search date October 2022) were searched, with no language restrictions. PARTICIPANTS/MATERIALS, SETTING, METHODS: Randomized controlled trials (RCTs) and cohort studies comparing a pET guided by TER vs standard embryo transfer (sET) in different subgroups that undergo ART were identified. We also investigated pET in non-receptive-TER vs sET in receptive-TER, and pET in a specific population vs sET in a general population. Risk of bias (RoB) was assessed with the Cochrane tool and ROBINS-I. Only those with low/moderate RoB underwent meta-analysis. The GRADE approach was used to evaluate the certainty of evidence (CoE). MAIN RESULTS AND THE ROLE OF CHANCE: We screened 2136 studies and included 35 (85% used ERA and 15% used other TER). Two studies were RCTs comparing endometrial receptivity analysis (ERA)-guided pET vs sET in women with no history of RIF. In women without RIF, no important differences (moderate-CoE) were found in live birth rates and clinical pregnancy rates (CPR). We also performed a meta-analysis of four cohort studies that were adjusted for confounding. In agreement with the RCTs, no benefits were found in women without RIF. However, in women with RIF, low CoE suggests that pET might improve the CPR (OR 2.50, 95% CI 1.42-4.40). LIMITATIONS, REASONS FOR CAUTION: We found few studies with low RoB. Only two RCTs in women without RIF were published, and none in women with RIF. Furthermore, the heterogeneity observed in populations, interventions, co-interventions, outcomes, comparisons, and procedures limited the pooling of many of the included studies. WIDER IMPLICATIONS OF THE FINDINGS: In the population of women without RIF, in agreement with previously published reviews, pET did not prove to be more effective than sET and, therefore, it precludes the routine use of this strategy in this population until more evidence is available. However, more research is advisable in women with RIF as low-certainty evidence from observational studies adjusted for confounders suggests that the CPR might be higher with pET guided by TER in this population. Although this review presents the best available evidence, it is still insufficient to change current policies. STUDY FUNDING/COMPETING INTEREST(S): No specific funding was obtained for this study. There are no conflicts of interest to declare. REGISTRATION NUMBER: PROSPERO CRD42022299827.

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OBJECTIVE: This study sought to evaluate the influence of time (early <90 days and late >90 days) and endometrial injury on pregnancy success. METHODS: This is a retrospective study in which all infertile women who underwent at least one in vitro fertilization cycle at Clinica Gera between 2010 and 2015 were considered for inclusion. We included patients with a normal ovarian reserve and regular menses at intervals of up to 30 days. A total of 315 patient files were reviewed, and the study group was composed of patients who faced fertility issues and had male-caused infertility or idiopathic infertility. Also, women with male or unknown cause of infertility who have performed endometrial biopsy and have undergone embryo transfer up to 180 days after this procedure between 2010 and 2015 were included. The patients were divided into two groups according to the interval between biopsy and embryo transfer: group 1 (early-an interval of <90 days) and group 2 (late-an interval of >90 days and up to 180 days). RESULTS: The results were superior for the group with an interval of less than 90 days relative to the group with an interval of more than 90 days (p<0.04). The pregnancy rates for group 1 and group 2 were 58.5% and 43.4%, respectively. The odds ratio for pregnancy success was 1.63 (95% confidence interval: 1.04 to 2.55). CONCLUSION: The early transfer of embryos (<90 days) may produce better results with a high rate of pregnancy. Further studies are necessary to identify the mechanism involved in this phenomenon.

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OBJECTIVE: The use of frozen embryos in the treatment of infertility with assisted reproductive techniques has been increased. Different methods are used to prepare the endometrium for frozen embryo transfer (FET). The aim of this study was to compare pregnancy outcomes after treatment with tamoxifen and hormonal replacement therapy (HRT) in FET. METHODS: This randomized clinical trial was carried out with 214 infertile women in the infertility research center of Milad Hospital in Mashhad during 2018-2020. We had 84 patients receiving tamoxifen and 92 took HRT. Endometrial thickness (ET) and pregnancy outcome were measured in both groups. RESULTS: Mean infertility duration (p=0.328), number of embryos (p=0.649), FSH (p=0.390), LH (p=0.051) and LH/FSH ratio (p=0.287) as well as type of infertility (primary or secondary) (p=0.295), causes of infertility (p=0.750) and pattern of menstruation (p=0.676) were not significantly different in the two groups. Mean ET in the TMX and HRT groups were 8.72±1.45mm and 9.00±1.69mm, respectively (p=0.423). There was no statistically significant difference between chemical pregnancy (p=0.663), clinical pregnancy (p=0.994) and ongoing pregnancy (p≥0.999) in the TMX and HRT groups. CONCLUSIONS: Treatment with tamoxifen can be as effective as GnRH agonist for endometrial preparation in FET.

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