Importance Women with polyendocrine metabolic ovarian syndrome (PMOS) have elevated rates of pregnancy loss, but the contribution of aneuploidy is unclear. Objective We aimed to systematically review and conduct meta-analyses of the effects of PMOS on aneuploidy rates in eggs, preimplantation embryos, and pregnancy losses (PROSPERO: CRD42024590377). Evidence Review PubMed, Web of Science, and Scopus were searched until 4th March 2026. Included studies reported aneuploidy rates in women diagnosed with PMOS under the Rotterdam, NIH, or AE-PCOS guidelines and women without PMOS. Studies including parents with structural translocations were excluded. Risk of bias was assessed using a modified Newcastle Ottawa scale and certainty of evidence was assessed using Grading of Recommendations, Assessment, Development and Evaluation (GRADE). Studies were screened, assessed for risk of bias, and assessed for certainty of evidence by two independent reviewers. Disagreements were discussed until a consensus was reached. The primary outcomes in meta-analyses were aneuploidy, complex aneuploidy, and mosaicism, and data were synthesized with random-effects meta-analyses. Findings Twelve of 2,270 studies screened were included. Aneuploidy rates were reported for eggs (one retrospective study), pregnancy losses (one prospective and three retrospective cohort studies; 808 pregnancy losses), and preimplantation embryos (one prospective and six retrospective cohort studies; >5,600 embryos from 1,774 women). Meta-analysis showed that aneuploidies were not statistically different in pregnancy losses (odds ratio [OR]: 0.55, 95% confidence interval [CI]: 0.22 – 1.37) or preimplantation embryos (OR: 0.81, 95% CI: 0.57–1.15) from women of all ages with PMOS compared with those without. In studies that allowed stratification by maternal age, aneuploidy was significantly reduced in preimplantation embryos from women with PMOS <38 years of age (0.66, 95% CI: 0.54–0.80). Complex aneuploidies were decreased in preimplantation embryos from women of all ages with PMOS (OR: 0.59, 95% CI: 0.38–0.91). There were no differences in the odds of mosaicism in preimplantation embryos from women with PMOS (OR: 1.41, 95% CI: 0.83–2.39). This review was restricted by the small number of studies, limited information about maternal ages, and no information regarding parental origins of aneuploidy. Conclusion and relevance Below the age of 38, preimplantation embryos from women with PMOS have significantly lower odds of aneuploidy compared with women without PMOS. This difference may be lost with further advancing maternal age and could suggest alterations to the U-curve of aneuploidy for women with PMOS. Therefore, factors other than embryonic aneuploidy must contribute to the elevated rates of pregnancy loss reported in this group.

The leading cause of human pregnancy loss is aneuploidy, often tracing to errors in chromosome segregation during female meiosis1,2. Although abnormal crossover recombination is known to confer risk for aneuploidy3,4, limited data have hindered understanding of the potential shared genetic basis of these key molecular phenotypes. To address this gap, we performed retrospective analysis of pre-implantation genetic testing data from 139,416 in vitro fertilized embryos from 22,850 sets of biological parents. By tracing transmission of haplotypes, we identified 3,809,412 crossovers, as well as 92,485 aneuploid chromosomes. Counts of crossovers were lower in aneuploid versus euploid embryos, consistent with their role in chromosome pairing and segregation. Our analyses further revealed that a common haplotype spanning the meiotic cohesin SMC1B is associated significantly with both crossover count and maternal meiotic aneuploidy, with evidence supporting a non-coding cis-regulatory mechanism. Transcriptome- and phenome-wide association tests also implicated variation in the synaptonemal complex component C14orf39 and crossover-regulating ubiquitin ligases CCNB1IP1 and RNF212 in meiotic aneuploidy risk. More broadly, variants associated with aneuploidy often showed secondary associations with recombination, and several also exhibited associations with reproductive ageing traits. Our findings highlight the dual role of recombination in generating genetic diversity, while ensuring meiotic fidelity.

Background Premature ovarian insufficiency (POI) is characterized by the progressive decline of ovarian function before the age of 40 years, classically presenting with menstrual irregularities paired with elevated FSH, affecting approximately 1-4% of women worldwide. The aetiology is complex and causes range from chromosomal and autoimmune factors to iatrogenic forms, but most non-syndromic cases are thought to have a genetic basis. To date, numerous genes have been implicated, and familial clustering strongly supports high heritability. However, despite technological advances, it is difficult to identify causal genetic variants for most patients, indicating that many cases of POI could have a polygenic background. Given the significant impact of POI on fertility and health, a comprehensive synthesis of current genetic findings is needed. Objective and rationale The objective of this systematic review is to provide a comprehensive synthesis of genes and genomic regions implicated in non-syndromic POI. The primary outcome was genes or genetic loci associated with POI. Contrary to earlier systematic reviews on female infertility, we included both monogenic and polygenic studies, as well as patients with primary and secondary amenorrhea, to provide an overview of the diverse genetic landscape of non-syndromic POI. Search methods A systematic literature search was conducted in PubMed, Scopus, Web of Science, and Embase. Publications up to 13 February 2026 that investigated genetic causes of non-syndromic POI and were written in English were included. Studies limited to animal experimentation were excluded, as were reviews, meta-analyses, and non-peer reviewed material, such as abstracts and conference proceedings. Outcomes This systematic review identified 432 eligible studies from an initial pool of 5,586 records, encompassing both hypothesis-free and candidate-gene approaches, including a total of 47,680 individuals with non-syndromic POI. Across all studies, 859 genes and 102 unique genomic regions were implicated in POI. Most studies were classified as candidate-gene investigations, whereas approximately one-in-six studies employed hypothesis-free approaches. Quality assessment of hypothesis-free studies showed primarily moderate to poor methodological quality. From the hypothesis-free studies, 422 genes were linked to non-syndromic POI, 120 of which clustered with functionality in DNA recombination. Twenty-five genes showed moderate genetic evidence for a role in POI and were enriched in pathways related to meiosis, DNA repair, and female gamete development. Despite substantial research activity, approximately nine out of ten non-syndromic patients remained without a recognised genetic aetiology. Wider implications As most patients with non-syndromic POI lack a single causal variant, evidence suggests the condition with secondary amenorrhea could be largely polygenic and shaped by the combined effects of multiple genetic factors and their interaction with non-genetic influences. A focus on monogenic causes could overlook patients with high polygenic burden. Future genetic studies on POI should examine both monogenic and polygenic risk variants and investigate genetic differences across POI subtypes. Such strategies will be critical for improving genetic diagnosis, risk stratification, and the development of personalized reproductive care. Registration number Prospero - CRD42023469800

Germline mutations are heritable; they occur before the formation of a fertilized egg and are found in all cells. They can be detected through somatic tissue sampling, and de novo mutations (DNMs) are well-studied. The majority of known DNMs originate in paternal cells, but some include maternal contributions as well. Certain kinds of DNMs prevent a fertilized egg from developing to term, and these are much less well-characterized. Some also lack sequence variants in certain genes and some are never observed in a homozygous form; these are also not well studied. Recombination failure can cause aneuploidies (trisomies or monosomies), and an estimated half of pregnancy losses are explained by this phenomenon. Early pregnancy loss is understudied, and there are few therapeutic interventions. This study, the Copenhagen Pregnancy Loss (COPL) study, was designed to contribute to the understanding of pregnancy loss through trios of patients (mother, father, and fetus) with clinically diagnosed pregnancy loss, attempting to document sequence diversity and interplay between meiotic recombination and point mutations. This study included 664 cases of early pregnancy loss with 1439 fetal samples (multiple were collected from each loss, where possible). In 467 of the 664 cases, there was at least 1 fetal sample and 1 sample from both parents. A total of 59 losses indicated a higher-than-expected kinship with the mother, and 11 indicated a higher kinship with the father. Whole-genome sequencing (WGS) was used to assess aneuploidies, and detected them in 206 cases. Of these, monosomy X and trisomy 16 were the most common. In addition, 19 large de novo copy number variants (CNVs) were detected in 14 loss cases, none of which were near a common fragile site. Of these 14 cases, 11 were euploid losses and 6 contained aneuploidies. Failure at meiosis I results in the presence of both homologous chromosomes from the same parent. An estimated 27.2% of paternal and 32.3% of maternal triploidies occur at recombination hotspots, supporting the idea of meiosis failure. A total of 15,086 DNMs were pinpointed as paternal and 5967 as maternal, consistent with previous literature supporting a high paternal contribution to DNMs. Consistent with this, paternal triploidies showed a proportionally higher paternal fraction of phased mutations. DNMs shown in maternal triploidies indicated a lower paternal fraction than euploid fetuses. In addition, there was no correlation between sister/homologous state differences for high-AB DNMs in paternal triploidies. When searching for pathogenic single-site variants (SSVs) in the DNMs, 26 genotypes were found that were pathogenic or likely pathogenic; a total of 23 were DNMs and 3 were biallelic predicted loss-of-function variants (pLoF). The frequency of pathogenic SSVs in early pregnancy loss was higher compared with controls [odds ratio (OR) 2.98, P=5.7×10-6), and this effect remained after correction for parental age. These results showed probable genetic causes for pregnancy loss in 254 of 467 cases, including aneuploidies, triploidies, pathogenic SSVs, and de novo CNVs. Most of the genetic causes of loss originated on maternal chromosomes, and fetuses with triploidies had significantly more DNMs than fetuses that were euploid. These results indicate significant sequence diversity in early pregnancy loss, with additional diversity likely present but unidentified in the stages between implantation and clinically recognized pregnancy. Future research should focus on potential explanations for early pregnancy loss that cannot be explained by genetic causes, as well as on potential interventions for these cases.

Pathogenic variants in FANCM have been implicated in premature ovarian insufficiency, suggesting a critical role for FANCM in early germline development. To investigate this gene’s function in a controlled system, we evaluated whether a mouse in vitro primordial germ cell (PGC) model could be used to interrogate the consequences of FANCM loss on germ cell specification. Using CRISPR-Cas9 gene editing, we introduced a premature stop codon into exon 1 of Fancm in mouse embryonic stem cells. These edited cells were differentiated into epiblast-like cells and subsequently into primordial germ cell-like cells (PGCLCs), which were assessed for their developmental competence. After successful generation of in vitro -derived PGCLCs, we found that loss of FANCM markedly reduced PGCLC formation, consistent with previously reported in vivo phenotypes. Our findings demonstrate that this in vitro system provides a tractable platform for dissecting gene function in otherwise inaccessible stages of germline development. Moreover, our data suggest that FANCM is required at the earliest stages of PGC specification, potentially as early as the developmental window equivalent to embryonic day 8.5, a period not previously examined in vivo . ### Competing Interest Statement AP received grants (payments to institution) from Gedeon Richter, Ferring Pharmaceuticals, and Merck A/S; consulting fees from Novo Nordisk, Ferring Pharmaceuticals, Gedeon Richter, Cryos, and Merck A/S; and payment for lectures/presentations from Gedeon Richter, Ferring Pharmaceuticals, Merck A/S, Organon, and Abbott. ERH declares no conflicts of interest. She is a co-founder and shareholder of OvartiX Ltd and within the past five years, she has received honorariums for giving scientific talks on independent research from Merck, Ferring Pharmaceuticals, the Japanese Society for Reproductive Medicine, the Takeda Foundation, and IBSA. She has received funding for research through the University of Copenhagen from Interreg, Horizon 2020, the European Research Council, the Novo Nordisk Foundation, and the Independent Research Foundation Denmark. All other authors have nothing to declare. Novo Nordisk Foundation, https://ror.org/04txyc737, NNF21OC0066487, NNF22OC0073038, NNF22OC0074308 Danish National Research Foundation, https://ror.org/00znyv691, DNRF115 Wellcome Trust, https://ror.org/029chgv08, 316959/Z/24Z European Research Council, https://ror.org/0472cxd90, hypomethGENOME, 101161245, 724718-ReCAP DFF, 113-00003B, DFF-FSS 0134-00299B Lundbeck (Denmark), https://ror.org/0564cd633, R347-2020-2177

OBJECTIVE:To study whether a machine learning algorithm can effectively predict fetal genetic status, aneuploid or euploid, in cases of pregnancy loss, based solely on readily available clinical data. Accurate early prediction may enable improved clinical decision-making and personalized patient management. DESIGN:Prospective multicenter cohort study within the Copenhagen Pregnancy Loss study, with a development cohort (n = 788) from Copenhagen University Hospital Hvidovre and external validation cohorts from Copenhagen University Hospitals Herlev (n = 229) and North Zealand (n = 199). Enrollment was from November 2020 to May 2022. SUBJECTS:Women ≥18 years with confirmed intrauterine pregnancy loss before 22 weeks at three Danish Copenhagen University Hospitals. EXPOSURE:Ploidy status was determined using cell-free fetal deoxyribonucleic acid analysis from maternal blood. Forty-five clinical predictors, including anthropometric data, medical history, lifestyle factors, and partner information, were analyzed using a gradient boosted model. Feature importance was interpreted through SHapley Additive exPlanations analysis to elucidate key prognostic indicators. MAIN OUTCOME MEASURES:Model discrimination capability assessed by area under the receiver operating characteristic curve and area under the precision-recall curve, sensitivity, specificity, and calibration across cohorts. RESULTS:The machine learning model demonstrated moderate discriminative ability with a cross-validated area under the receiver operating characteristic curve of 0.69 (95% confidence interval 0.65-0.73) in the development cohort, maintaining equivalent performance in external validations. At a 90% specificity threshold, sensitivity was 54.4% in the development cohort (Hvidovre), 47% at Herlev, and 48% at North Zealand. Key predictors included maternal age, gestational age, paternal age, body mass index, vitamin D supplementation, and vitamin E supplementation. CONCLUSION:This study represents the first machine learning approach to distinguish euploid from aneuploid pregnancy losses using clinical data alone, providing a framework for earlier recognition of women with treatable conditions before multiple losses occur. Novel associations between vitamin supplementation and ploidy status invite further mechanistic investigation. However, moderate discriminative performance and population-specific factors highlight the need for additional validation and exploration before clinical integration.

Triploid and haploid conceptions are not viable and are a common occurrence in humans, where they account for 10% of all pregnancy losses. Despite the parent of origin being important in the etiology of the pregnancy, our knowledge of their causes is limited, especially at the point of conception. Using a dataset of 96,660 biopsies and a validation dataset of 44,324 from human blastocyst embryos generated by intracytoplasmic sperm injection, we estimate that 1.1% of human conceptions (n = 1,063) contain extra or missing chromosome sets in zygotes. In our cohort of intracytoplasmic-sperm-injection-derived embryos, where the risk of polyspermy is inherently lower compared to natural conception, we identify for the first time a maternal age effect, with a 1.046-per-year increased risk in triploidy/haploidy (p < 0.001). In 0.03% of couples, we identified three or more triploid/haploid embryos, suggesting a personal risk effect (p = 0.03). Genotype analysis of 41 triploid embryo biopsies and their parents shows that around one-third of maternal triploid conceptions originate in meiosis I and two-thirds in meiosis II. Seven of these embryos are inferred to have entirely failed to initiate meiotic recombination genome wide, a surprising finding suggesting that human oocytes with pervasive meiotic recombination failure that are formed during fetal development are capable of ovulation in adult life. Finally, we identify a type of genome-wide maternal isodiploidy (two maternal chromosome sets) in 0.05% of embryos (41/74,009). Collectively, our findings shed light on the biology of meiosis and the formation of human oocytes with the number of chromosome sets.

Menopause not only signifies the end of a woman's reproductive life, but also brings about significant changes in both mental and physical health due to hormonal changes. Age of natural menopause (ANM) and reproductive lifespan is determined by the formation and subsequent depletion of follicles in females. In this study, we identified a robust association between a common functional missense variant in PARP1 and age at menopause in a sample of 201,323 women. Using an in vitro model to generate primordial germ cells - the precursors of sperm and oocytes- we report that Parp1 affects PGCs in two different ways. Our identified missense variant (V762A) significantly reduces the germ cell population by enhanced DNA binding resulting in increased apoptosis. Conversely, deletion of Parp1 results in an increased population of PGCs and proteomic analysis revealed that transcription factors that drive PGC formation show increased expression in precursor cells. This is caused by increased transcription of Rhox genes (Rhox2A, Rhox6 and Rhox9), implicating Parp1 in downregulation of genes that determine PGC fate. We propose that Parp1 regulates PGC fate and that its increased chromatin association ("trapping") causes a decreased population of PGCs, thereby providing a molecular cause of the earlier onset menopause on female carriers of the variant. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement ERH: The research was funded by the Danish National Science Foundation (grant DNRF115), the Novo Nordisk Foundation (NNF21OC0066487, NNF22OC00734308); the Wellcome Trust Discovery Award (HERA; 316959/Z24/Z and 302536/Z/23/Z); Vera and Carl Johan Michaelsens Legat (001946); Jason Halliwell was funded by a Lundbeck Foundation Postdoctoral Fellowship (R347-2020-2177). JRBP was funded by the Medical Research Council (unit programs: MC\_UU\_12015/2, MC\_UU\_00006/2); JVO and MLN were funded by the Novo Nordisk Foundation grants NNF14CC0001 and NNF24SA0098829. This project was also supported by a generous grant from the Danish Agency of Higher Education and Science to establish the PLATO research infrastructure: Danish National Mass Spectrometry Platform for Proteomics and Biomolecular Imaging (grant no. 5229-00012B). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study used openly available human data originally located at https://www.reprogen.org/data_download.html (common variants). The exome sequencing look up is available from the supplementary data in Stankovich et al 2024 (doi: 10.1038/s41586-024-07931-x). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors

Introduction The Cardiometabolic function in Offspring, Mother and Placenta after Assisted Reproductive Technology (COMPART) study is a prospective cohort study aiming to explore health outcomes in mothers and children following assisted reproductive technology (ART), with a particular focus on frozen embryo transfer (FET) versus fresh embryo transfer (fresh-ET). The increasing prevalence of ART and FET emphasises the need to assess potential health risks associated with the procedures, both in pregnancy, such as pre-eclampsia and large for gestational age offspring, and in the children, such as obesity and cardiometabolic dysfunction.Methods and analysis The cohort will include 600 pregnant women, their potential partner and their offspring in a 1:1:1 ratio of pregnancies achieved after ART with FET, ART with fresh-ET and women who conceived naturally. The study will involve extensive data collection from electronic medical records; parental questionnaires; biochemical, genetic and epigenetic analyses in blood, urine and placental tissue; and medical imaging (fetal ultrasound and PEA POD scan) and clinical examinations. Outcomes are grouped into six work packages (WPs) related to fetal growth (WP1), pregnancy (WP2), placenta (WP3), offspring (WP4), genetics (WP5) and epigenetics (WP6).Ethics and dissemination The COMPART study aims to provide valuable insights into the impact of ART and FET on maternal and offspring health and the underlying mechanisms responsible. The study seeks to advance reproductive medicine, shape clinical practice and guidelines and ultimately ensure maternal-fetal health following ART. The study has been approved by the Danish Ethics Committee (H-23071266; February 2024).Trial registration number NCT06334003

In order to make clinical recommendations based on uncertain evidence, a systematic review and meta-analysis on the influence of micronutrient supplementation on preclinical and clinical reproductive outcomes was undertaken. PubMed and Scopus were searched until 12 November 2024. Parallel-grouped intervention studies with women undergoing fertility treatment with micronutrient supplementation or addition of micronutrient to in-vitro maturation media were included. The primary outcomes were oocyte maturation and chromosome aneuploidy rates, pregnancy rate, miscarriage rate, and live birth rate. Five of 1810 studies were included. In three clinical studies, 326 women underwent fertility treatment with coenzyme Q10 (CoQ10) or control treatment. CoQ10 increased oocyte retrieval and live birth rates for women diagnosed with poor ovarian response (POR; OR = 2.28), and increased the pregnancy rate for women diagnosed with POR or polycystic ovary syndrome (PCOS) (OR = 2.20 and 13.26, respectively). CoQ10 had no effect on the miscarriage rate. In two in-vitro studies, 127 women donated 241 immature oocytes which were matured with CoQ10 or resveratrol. CoQ10 increased the oocyte maturation rate (OR = 2.73), and decreased oocyte and chromosome aneuploidy rates (OR = 0.31 and 0.57, respectively) for women of advanced maternal age (AMA). Resveratrol had no effect. Women of AMA and women diagnosed with POR or PCOS gained greater benefit from CoQ10 supplementation.

Every generation, the human genome is shuffled during meiosis and a single fertilized egg gives rise to all of the cells of the body1. Meiotic errors leading to chromosomal abnormalities are known causes of pregnancy loss2,3, but genetic aetiologies of euploid pregnancy loss remain largely unexplained4. Here we characterize sequence diversity in early pregnancy loss through whole-genome sequencing of 1,007 fetal samples and 934 parental samples from 467 trios affected by pregnancy loss (fetus, mother and father). Sequenced parental genomes enabled us to determine both the parental and meiotic origins of chromosomal abnormalities, detected in half of our set. It further enabled us to assess de novo mutations on both homologous chromosomes from parents transmitting extra chromosomes, and date them, revealing that 6.6% of maternal mutations occurred before sister chromatid formation in fetal oocytes. We find a similar number of de novo mutations in the trios affected by pregnancy loss as in 9,651 adult trios, but three times the number of pathogenic small (<50 bp) sequence variant genotypes in the loss cases compared with adults. Overall, our findings indicate that around 1 in 136 pregnancies is lost due to a pathogenic small sequence variant genotype in the fetus. Our results highlight the vast sequence diversity that is lost in early pregnancy.

(Abstracted from Nature 2025;642(8068):672–681) Mutations in germ cells are passed from parent to child and occur before fertilization; variations can be evaluated using somatic tissue samples, and germline mutations that appear de novo in offspring (DNMs) have been studied extensively. Many DNMs are paternal, but some have nearly equal maternal and paternal contribution.

The leading cause of human pregnancy loss is aneuploidy, often tracing to errors in chromosome segregation during female meiosis. While abnormal crossover recombination is known to confer risk for aneuploidy, limited data have hindered understanding of the potential shared genetic basis of these key molecular phenotypes. To address this gap, we performed retrospective analysis of preimplantation genetic testing data from 139,416 in vitro fertilized embryos from 22,850 sets of biological parents. By tracing transmission of haplotypes, we identified 3,656,198 crossovers, as well as 92,485 aneuploid chromosomes. Counts of crossovers were lower in aneuploid versus euploid embryos, consistent with their role in chromosome pairing and segregation. Our analyses further revealed that a common haplotype spanning the meiotic cohesin SMC1B is significantly associated with both crossover count and maternal meiotic aneuploidy, with evidence supporting a non-coding cis-regulatory mechanism. Transcriptome- and phenome-wide association tests also implicated variation in the synaptonemal complex component C14orf39 and crossover-regulating ubiquitin ligases CCNB1IP1 and RNF212 in meiotic aneuploidy risk. More broadly, recombination and aneuploidy possess a partially shared genetic basis that also overlaps with reproductive aging traits. Our findings highlight the dual role of recombination in generating genetic diversity, while ensuring meiotic fidelity.

The Danish Monozygotic Twin Study on Migraine is a population-based twin study established in 2023–2024. The cohort was created to lay the foundation for innovative studies of the role of environmental, genetic, and epigenetic factors and their complex interactions in the pathogenesis of migraine. The aim of this paper is to describe data collection, content, characteristics of participants and to assess the representativeness of the cohort by comparing participants to non-responders. Danish monozygotic twins born between 1967 and 2000 were invited to participate. Self-reported questionnaires were sent out to 9,036 possible participants. The questionnaires assessed migraine and migraine subtypes, life satisfaction, resilience, stress, childhood trauma and the relationship of the participant to their family. Through linkage to the nationwide Danish registries the cohort contains individual level information on education, income, patient data from hospitals, prescription medication and childbirth. The Danish registries also enable longitudinal data collection on health outcomes. Individuals who responded to the migraine questionnaire were defined as participants. The cohort consists of 3,893 individuals, including 1,822 complete twin pairs, 1,173 individuals with migraine and 280 migraine discordant twin pairs. 123 participants were included in a substudy with a migraine diagnostic interview and collection of blood samples for both genetic and epigenetic studies. Comparison between participants and non-responders showed a higher participation rate among women. For both genders participants were older, had a higher level of education and a higher level of income compared to non-responders. Sociodemographic differences in participation should be considered to avoid biased estimates in future studies based on the cohort.

IMPORTANCE:Advances in the treatment of childhood cancer have significantly improved survival rates, with more than 80% of survivors reaching adulthood. However, gonadotoxic cancer treatments endanger future fertility, and prepubertal males have no option to preserve fertility by sperm cryopreservation. In addition, boys with cryptorchidism are at risk of compromised fertility in adulthood. OBJECTIVE:To investigate current evidence for male fertility restoration strategies, explore barriers to clinical implementation, and outline potential steps to overcome these barriers, a scoping review was conducted. This knowledge synthesis is particularly relevant for prepubertal male cancer survivors and boys with cryptorchidism. EVIDENCE REVIEW:The review was conducted after the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews criteria and previously published guidelines and examined studies using human testis tissue of prepubertal boys or healthy male adults. A literature search in PubMed was conducted, and 72 relevant studies were identified, including in vivo and in vitro approaches. FINDINGS:In vivo strategies, such as testis tissue engraftment and spermatogonial stem cell transplantation, hold promise for promoting cell survival and differentiation. Yet, complete spermatogenesis has not been achieved. In vitro approaches focus on the generation of male germ cells from direct germ cell maturation in various culture systems, alongside human induced pluripotent stem cells and embryonic stem cells. These approaches mark significant advancements in understanding and promoting spermatogenesis, but achieving fully functional spermatozoa in vitro remains a challenge. Barriers to clinical implementation include the risk of reintroducing malignant cells and introduction of epigenetic changes. CONCLUSION:Male fertility restoration is an area in rapid development. On the basis of the reviewed studies, the most promising and advanced strategy for restoring male fertility using cryopreserved testis tissue is direct testis tissue transplantation. RELEVANCE:This review identifies persistent barriers to the clinical implementation of male fertility restoration. However, direct transplantation of frozen-thawed testis tissue remains a promising strategy that is on the verge of clinical application.

The timing of DNA replication in mammals is crucial for minimizing errors and influenced by genome usage and chromatin states. Replication timing in the newly formed mammalian embryo remains poorly understood. Here, we have investigated replication timing in mouse zygotes and 2-cell embryos, revealing that zygotes lack a conventional replication timing program, which then emerges in 2-cell embryos. This program differs from embryonic stem cells and generally correlates with transcription and genome compartmentalization of both parental genomes. However, consistent and systematic differences existed between the replication timing of the two parental genomes, including considerably later replication of maternal pericentromeric regions compared to paternal counterparts. Moreover, maternal chromatin modified by Polycomb Repressive Complexes in the oocyte, undergoes early replication, despite belonging to the typically late-replicating B-compartment of the genome. This atypical and asynchronous replication of the two parental genomes may advance our understanding of replication stress in early human embryos and trigger strategies to reduce errors and aneuploidies. Here, the authors reveal the emerging replication timing program in mouse zygotes and 2-cell embryos, which differs from embryonic stem cells. They find systematic differences between the replication timing of the two parental genomes at pericentromeric regions and Polycomb target sites.

Isthmocele, a complication of Cesarean Delivery (CD), is associated with postmenstrual spotting, secondary infertility, cesarean scar pregnancies, and abnormal placentation. The extent isthmocele is associated with development of placenta accreta spectrum (PAS) is unknown and existing data is mostly retrospective. This study aims to determine the relationship between isthmocele and development of PAS. A retrospective study was conducted at a National Accreta Center from January 1, 2012 through September 30, 2022. All patients with a history of CD and confirmed PAS were identified and compared to patients who did not develop PAS and underwent repeat CD. Ultrasounds were reviewed for presence, size, and appearance of isthmocele, as well as associated prenatal and demographic information. Statistical analysis included T test and Chi square with P< 0.05 considered significant when comparing the two study groups. We identified 137 patients with a history of CD who went on to develop PAS. Among those who had early ultrasound images for review, there were 23 patients who developed PAS after CD compared to 70 patients who had normal placentation. There were no differences in age and number of prior CDs across study groups. Patients who developed PAS were nearly 6 times as likely to have an isthmocele on early US (p=0.002). Notably, every patient with early implantation in the lower half of the uterus ultimately developed PAS whereas those patients with implantation in the upper half of the uterus did not irrespective of isthmocele diagnosis. Isthmoceles diagnosed on early US are associated with a significantly increased risk of PAS. Our study highlights the importance that accurate identification of early implantation in the lower uterine segment has in prediction of development of PAS in patients with history of CD. Prospective studies are critically necessary in order to evaluate isthmocele as an independent risk factor for development of PAS.

Abstract Study question What is the proportion of the genome where the egg and the first or second polar bodies descend from the same maternal homolog? Summary answer The egg is about 30% identical to a random haploid genome from the first polar body and about 40% identical to the second polar body. What is known already After crossing over, human female meiosis generates three products: the first polar body (PBI) splits first with two sister chromatids per chromosome; the second polar body (PBII) and the egg split next, each with a single set of chromatids. When meiosis proceeds normally, the egg must be identical (i.e., same maternal homolog) to PBII at the centromeres. However, the proportion of the entire genome where the egg is identical to PBII (or to a random chromatid set from PBI), while being a fundamental property of meiosis, is not intuitively clear and has not been empirically studied. Study design, size, duration We used both theoretical and empirical approaches. We first derived formulas and performed simulations for the identity between the egg and the polar bodies, with or without modeling crossover interference. We then analyzed genotype data from seven egg/PBI/PBII trios and 43 triploid embryos. Finally, we analyzed 8,476 dizygotic twin pairs from research-consented 23andMe, Inc. customers in an attempt to find PBII twins, who would (hypothetically) share maternal genetic material in all centromeres. Participants/materials, setting, methods The egg/PBI/PBII trios came from three female donors and were genotyped at about 300k SNPs (Ottolini et al, Nat Genet, 2015). Embryos were sequenced to depth about 0.05x for routine PGT-A and identified as triploid upon retrospective analysis with LD-PGTA (Ariad et al, Genome Res, 2023). Coverage-based analysis confirmed triploidy predictions for XXY embryos. The DZ twin pairs were genotyped at about 640k SNPs and self-reported dates of birth within two days of each other. Main results and the role of chance In an infinitely long chromosome, the egg would be identical to PBII, or to a random chromatid from PBI, in only a third of its length. Modeling recombination using the human female genetic map and assuming no interference predicted that the egg would be on average 53% identical to PBII and 24% identical to a random haploid genome from PBI. We confirmed these estimates with simulations. However, in seven egg/PB1/PB2 trios, the egg was on average only 40% identical with PBII. Similarly, in 17 triploid embryos with an MII (likely-maternal) error, the two transmitted maternal chromosome sets were on average only 37% identical. Including crossover interference in the simulations reduced the identity between the egg and PBII to 42%, closer to the empirical observations. Hypothetical PBII twins would occur by two sperm from the same father fertilizing both the egg and PBII. They would share, based on the results above, an average of about 45% of their genomes. Such twins would also have identical maternal genetic material in all centromeres. In 8,476 genetically dizygotic twin pairs, only 67 shared at least one haplotype in all centromeres, not significantly more than expected by chance for dizygotic twins. Limitations, reasons for caution The empirical results are based on a small number of egg/PBI/PBII trios (n = 7) from only three donors. The number of triploid embryos was larger, but they were sequenced to very low depth, and the results for MI-error embryos showed much less sharing between the two maternal chromosomes than expected. Wider implications of the findings We show the fundamental and perhaps counter-intuitive result that the egg is only 30-40% identical to the polar bodies. This provides a reference against which deviations from normal crossover patterns could be evaluated in triploid and other aneuploid embryos. Polar body twins, if they occur, must be extremely rare. Trial registration number Not applicable