BACKGROUND: Monozygotic (MZ) twins are believed to arise from the fission of a single fertilized embryo at different stages. Monochorionic MZ twins, who share one chorion, originate from the splitting of the inner cell mass (ICM) within a single blastocyst. In the classic model for dichorionic MZ twins, the embryo splits before compaction, developing into two blastocysts. However, there are a growing number of ART cases where a single blastocyst transfer results in dichorionic MZ twins, indicating that embryo splitting may occur even after blastocyst formation.
OBJECTIVE: For monochorionic MZ twins, we conducted a comprehensive analysis of the cellular mechanisms involved in ICM splitting, drawing from both ART cases and animal experiments. In addition, we critically re-examine the classic early splitting model for dichorionic MZ twins. We explore cellular mechanisms leading to two separated blastocysts in ART, potentially causing dichorionic MZ twins.
METHODS: Relevant studies including research articles, reviews, and conference papers were searched in the PubMed database. Cases of MZ twins from IVF clinics were found by using combinations of terms including \'monozygotic twins\' with \'IVF case report\', \'ART\', \'single embryo transfer\', or \'dichorionic\'. The papers retrieved were categorized based on the implicated mechanisms or as those with unexplained mechanisms. Animal experiments relating to MZ twins were found using \'mouse embryo monozygotic twins\', \'mouse 8-shaped hatching\', \'zebrafish janus mutant\', and \'nine-banded armadillo embryo\', along with literature collected through day-to-day reading. The search was limited to articles in English, with no restrictions on publication date or species.
RESULTS: For monochorionic MZ twins, ART cases and mouse experiments demonstrate evidence that a looser ICM in blastocysts has an increased chance of ICM separation. Physical forces facilitated by blastocoel formation or 8-shaped hatching are exerted on the ICM, resulting in monochorionic MZ twins. For dichorionic MZ twins, the classic model resembles artificial cloning of mouse embryos in vitro, requiring strictly controlled splitting forces, re-joining prevention, and proper aggregation, which allows the formation of two separate human blastocysts under physiological circumstances. In contrast, ART procedures involving the transfer of a single blastocysts after atypical hatching or vitrified-warmed cycles might lead to blastocyst separation. Differences in morphology, molecular mechanisms, and timing across various animal model systems for MZ twinning can impede this research field. As discussed in future directions, recent developments of innovative in vitro models of human embryos may offer promising avenues for providing fundamental novel insights into the cellular mechanisms of MZ twinning during human embryogenesis.
CONCLUSIONS: Twin pregnancies pose high risks to both the fetuses and the mother. While single embryo transfer is commonly employed to prevent dizygotic twin pregnancies in ART, it cannot prevent the occurrence of MZ twins. Drawing from our understanding of the cellular mechanisms underlying monochorionic and dichorionic MZ twinning, along with insights into the genetic mechanisms, could enable improved prediction, prevention, and even intervention strategies during ART procedures.
UNASSIGNED: N/A.

In the last decades, to enhance success rates in assisted reproductive technology (ART) cycles, scientists have continually tried to optimize embryo culture and selection to increase clinical outcomes. In this scenario, the application of laser technology has increased considerably worldwide and is currently applied across ART in several ways: for assisted hatching (AH) or thinning of the zona pellucida (ZP), embryo biopsy, to immobilize and select the sperm during intracytoplasmic sperm injection, as well as to induce artificial blastocyst shrinkage before cryopreservation. Laser-AH has been suggested as a procedure to improve embryo implantation: the concept is that drilling holes through or thinning of the ZP could improve the hatching process and implantation. The artificial disruption of the ZP can be performed by different approaches: mechanically, chemically and with the laser, which is one of the most favourable and easy methods to remove part of the ZP and to augment the possibilities of implantation in patients defined as having a poor prognosis of success, or when the ZP is too thick. However, in the current literature, there is not sufficient evidence about the potential risk or impairment that laser utilization might induce on embryo development; therefore, the main aim of the current review is to provide an overview of the existing knowledge on the ZP and the mechanisms of manipulating it to improve the effectiveness of ART. Also, it emphasizes the positive aspect of laser application as a powerful tool that might increase the chance of pregnancy for infertile couples undergoing ART cycles.

暂无摘要。

This case report examines the difficulties faced by a couple with 11 years of primary infertility. Based on the diagnostic evaluation, it was determined that the male was a necrozoospermia patient, while the female had unilateral cornual blockage and polycystic ovarian syndrome (PCOS) with diabetes mellitus (DM) symptoms identified. A comprehensive approach was used in the treatment for the female patient, which included a gonadotropin-releasing hormone (GnRH) short antagonist protocol, a GnRH agonist (GnRHa) trigger, assisted hatching (AH), and the use of the hypo-osmotic swelling test (HOST) to gauge the viability of the sperm. The successful outcome, as evidenced by the increasing levels of beta-human chorionic gonadotropin (β-hCG) and a successful embryo transfer, highlights the effectiveness of a customized and multifaceted approach in managing intricate infertility problems. This instance offers insightful information about the way modern reproductive technologies can be successfully integrated with specialized treatment plans to achieve successful outcomes in difficult cases of infertility.

OBJECTIVE: To evaluate whether laser-mediated assisted hatching (AH) performed on vitrified/warmed blastocysts before embryo transfer can improve live birth rate.
METHODS: The \"pArtiaL zonA pelluciDa removal by assisteD hatchINg of blastocysts (ALADDIN)\" is a 2-center comparative study with a parallel randomized controlled design.
METHODS: University hospital.
METHODS: Participants were recruited between September 2018 and November 2021. They were aged 18-39 years, underwent nondonor in vitro fertilization cycles, and were scheduled for elective single embryo transfer with vitrified/warmed blastocysts. Those with uterine abnormalities, body mass index of >35 kg/m2, severe male factor infertility, or performing preimplantation genetic testing were excluded.
METHODS: Assisted hatching was performed using a 1,480 nm diode laser, removing approximately one-third of the zona pellucida with continuous 0.2 ms pulses applied from the 1-5 o\'clock positions.
METHODS: The primary outcome was the live birth rate. Secondary end points included clinical pregnancy, miscarriage, multiple pregnancies, preterm births, obstetric and neonatal complications, and congenital anomalies.
RESULTS: Overall, 698 participants met the inclusion criteria and were randomized: 352 patients were assigned to the AH arm and 346 to the control arm. Of the participants, 105 (29.8%) and 101 (29.2%), respectively, achieved a live birth after treatment. The relative risk of live birth in patients with vitrified/warmed blastocysts treated with AH was 1.02 (95% confidence interval, 0.86-1.19). Exploratory subgroup analyses for women\'s age, recruiting centers, indications for in vitro fertilization, method of insemination, blastocyst quality, and days of blastocyst development failed to highlight any clinical situation that could benefit from AH in thawed blastocysts.
CONCLUSIONS: In patients undergoing frozen embryo transfer with vitrified/warmed blastocysts, laser AH does not improve the live birth rate. Further studies are required to rule out milder but potentially interesting benefits in specific subgroups of patients.
BACKGROUND: ClinicalTrials.gov: NCT03623659.

The mammalian zygote, formed after a sperm fertilizes an egg, undergoes several rounds of mitosis and morphogenesis to form the blastocyst. During the peri-implantation period, the blastocyst hatches out of the zona pellucida (ZP) and invades the receptive uterine endometrium. This process promotes maternal-fetal dialogue at the physiological and molecular level, thereby initiating the implantation process. Blastocyst hatching is a consequence of elevated osmotic pressure due to active Na+/K+ ion transporter in the blastocyst cavity, as well as proteases produced by trophectoderm (TE) that hydrolyze the ZP. This review summarizes the process underpinning blastocyst hatching, such as the hatching schedule, the location of TEs during initial hatching out of the ZP, the molecules involved in blastocyst hatching, and how these processes affect implantation events. Additionally, we focus on identifying crucial molecules that may influence the quality of implantation and predict the outcome of embryo implantation. Further understanding the mechanism of these molecules may help us to improve the efficiency of Assisted reproductive technology (ART) in livestock breeding. This review provides insight into embryonic development, specifically during the short-term process of blastocyst hatching and its effects on the following implantation.

Does assisted hatching increase the cumulative live birth rate in subfertile couples with repeated implantation failure?
This study showed no evidence of effect for assisted hatching as an add-on in subfertile couples with repeated implantation failure.
The efficacy of assisted hatching, with regard to the live birth rate has not been convincingly demonstrated in randomized trials nor meta-analyses. It is suggested though that especially poor prognosis women, e.g. women with repeated implantation failure, might benefit most from assisted hatching.
The study was designed as a double-blinded, multicentre randomized controlled superiority trial. In order to demonstrate a statistically significant absolute increase in live birth rate of 10% after assisted hatching, 294 participants needed to be included per treatment arm, being a total of 588 subfertile couples. Participants were included and randomized from November 2012 until November 2017, 297 were allocated to the assisted hatching arm of the study and 295 to the control arm. Block randomization in blocks of 20 participants was applied and randomization was concealed from participants, treating physicians, and laboratory staff involved in the embryo transfer procedure. Ovarian hyperstimulation, oocyte retrieval, laboratory procedures, embryo selection for transfer and cryopreservation, the transfer itself, and luteal support were performed according to local protocols and were identical in both the intervention and control arm of the study with the exception of the assisted hatching procedure which was only performed in the intervention group. The laboratory staff performing the assisted hatching procedure was not involved in the embryo transfer itself.
Participants were eligible for inclusion in the study after having had either at least two consecutive fresh IVF or ICSI embryo transfers, including the transfer of frozen and thawed embryos originating from those fresh cycles, and which did not result in a pregnancy or as having had at least one fresh IVF or ICSI transfer and at least two frozen embryo transfers with embryos originating from that fresh cycle which did not result in a pregnancy. The study was performed at the laboratory sites of three tertiary referral hospitals and two university medical centres in the Netherlands.
The cumulative live birth rate per started cycle, including the transfer of fresh and subsequent frozen/thawed embryos if applicable, resulted in 77 live births in the assisted hatching group (n = 297, 25.9%) and 68 live births in the control group (n = 295, 23.1%). This proved to be statistically not significantly different (relative risk: 1.125, 95% CI: 0.847 to 1.494, P = 0.416).
There was a small cohort of subfertile couples that after not achieving an ongoing pregnancy, still had cryopreserved embryos in storage at the endpoint of the trial, i.e. 1 year after the last randomization. It cannot be excluded that the future transfer of these frozen/thawed embryos increases the cumulative live birth rate in either or both study arms. Next, at the start of this study, there was no international consensus on the definition of repeated implantation failure. Therefore, it cannot be excluded that assisted hatching might be effective in higher order repeated implantation failures.
This study demonstrated no evidence of a statistically significant effect for assisted hatching by increasing live birth rates in subfertile couples with repeated implantation failure, i.e. the couples which, based on meta-analyses, are suggested to benefit most from assisted hatching. It is therefore suggested that assisted hatching should only be offered if information on the absence of evidence of effect is provided, at no extra costs and preferably only in the setting of a clinical trial taking cost-effectiveness into account.
None.
Netherlands Trial Register (NTR 3387, NL 3235, https://www.clinicaltrialregister.nl/nl/trial/26138).
6 April 2012.
28 November 2012.

OBJECTIVE: This study aimed to retrospectively evaluate the efficacy of a hyaluronan-enriched transfer medium (HETM) for transfer failures and transfer of frozen embryos that have been graded as C at the time of transfer according to the Gardner classification of trophectoderm (TE).
METHODS: This study included 365 cycles of unsuccessful frozen-thawed embryo transfers in hormone replacement cycles graded C according to the Gardner classification of TE at the time of transfer. Clinical pregnancy rates were compared using the χ2 test, with the patients divided into two groups: one whose transfers did include HETM (HETM group) and one whose transfers did not include HETM (control group). As a subgroup analysis, patients with a TE grade of C at the time of transplantation were divided into two groups: those aged 39 years or younger and those aged 40 years or older at the time of transplantation. The clinical pregnancy rates of the groups with and without HETM were then compared.
RESULTS: No difference in the clinical pregnancy rates between the HETM and control groups was observed.
CONCLUSIONS: Hyaluronic acid is believed to favor implantation by promoting adhesion between the embryo and the endometrium, and there are reports of improved implantation and pregnancy rates as a result of HETM. However, the present results suggest limited effectiveness for HETM. Further case series should be conducted, and the suitability of its use as a treatment should be investigated.

OBJECTIVE: To determine if deep learning artificial intelligence algorithms can be used to accurately identify key morphologic landmarks on oocytes and cleavage stage embryo images for micromanipulation procedures such as intracytoplasmic sperm injection (ICSI) or assisted hatching (AH).
METHODS: Two convolutional neural network (CNN) models were trained, validated, and tested over three replicates to identify key morphologic landmarks used to guide embryologists when performing micromanipulation procedures. The first model (CNN-ICSI) was trained (n = 13,992), validated (n = 1920), and tested (n = 3900) to identify the optimal location for ICSI through polar body identification. The second model (CNN-AH) was trained (n = 13,908), validated (n = 1908), and tested (n = 3888) to identify the optimal location for AH on the zona pellucida that maximizes distance from healthy blastomeres.
RESULTS: The CNN-ICSI model accurately identified the polar body and corresponding optimal ICSI location with 98.9% accuracy (95% CI 98.5-99.2%) with a receiver operator characteristic (ROC) with micro and macro area under the curves (AUC) of 1. The CNN-AH model accurately identified the optimal AH location with 99.41% accuracy (95% CI 99.11-99.62%) with a ROC with micro and macro AUCs of 1.
CONCLUSIONS: Deep CNN models demonstrate powerful potential in accurately identifying key landmarks on oocytes and cleavage stage embryos for micromanipulation. These findings are novel, essential stepping stones in the automation of micromanipulation procedures.

At present, there is no standardised protocol for assisted hatching (AH) and the field is beset with contradictory data. We hypothesised that such contradiction may be related to inconsistencies in clinical practice. This study aimed to investigate the application, preferences, and variations of AH in current clinical practice prior to embryo transfer (AHpET) and biopsy (AHpBP). An online voluntary survey, consisted of 25 questions regarding different aspects of AH, was circulated amongst different fertility centres via newsletters between October 2019 and March 2020. One-hundred twenty-nine different fertility centres participated in the survey. AHpBP was widely used (90.6% [48/53]) amongst these centres, especially for trophectoderm biopsy (92.2% [47/51]). In contrast, only 64.6% (73/113) of centres administrated AHpET; the application of AHpET was even lower in UK-based centres (36.6% [15/41]). Although laser pulses have become the predominant technique for AH, significant variation existed in the precise strategy. Zona pellucida (ZP) drilling was the main method for AHpBP, whilst both ZP drilling and ZP thinning were applied equally for AHpET. Furthermore, the ZP manipulation varied widely with regards to the size of the ZP opening and the extension of ZP thinning. This is the first representative survey relating to the current practice of AH. Laser-assisted AH is used extensively, especially for AHpBP. However, there is significant disparity in clinical practice across different centres. Future research should aim to create a standardised protocol for AH to help reduce the evident variation in clinical practice and investigate the true value of AH.