Comparisons of cumulative live birth rates after embryo transfers at day 2/3 versus day 5/6: a French national study.

RESEARCH QUESTION: Are there significant differences between cumulative live birth rates (CLBR) after short or extended embryo culture when comparisons are performed per cycle? DESIGN: This French national study included all IVF cycles performed from January 2016 to December 2019 with at least one cleaved embryo at day 2. The day 2/3 and day 5/6 groups were identified using the National Biomedicine Agency register. Only attempts involving the vitrification method were included. CLBR was assessed with 1 and 2 years of follow-up using a logistic regression model. The evolution of CLBR per cycle was compared over 1 year of follow-up. RESULTS: In total, 133,250 cycles met the inclusion criteria (70,528 and 62,722 in the day 2/3 and day 5/6 groups). In multivariate analysis including several patient and cycle characteristics, the CLBR per cycle was significantly lower in the day 5/6 compared with the day 2/3 group. A significantly higher rate of fresh embryo transfer cancellation was observed in the day 5/6 compared with the day 2/3 group. The evolution of the CLBR was significantly different in favour of the day 2/3 group in cases with three or fewer day 2 embryos, whatever the patient's age, in their two first attempts as well as in their third or further attempts. CONCLUSIONS: Overall, the nationwide results per cycle suggest that extended embryo culture until the blastocyst stage, even when used in combination with vitrification, could not improve live birth rates. Moreover, where three or fewer day 2 embryos are obtained, it might be preferable to use the short embryo culture strategy.

Risk factors associated with preterm birth in singletons born after IVF: a national cohort study.

RESEARCH QUESTION: What are the risk factors for prematurity other than intrauterine growth restriction in singletons after IVF? DESIGN: Data were collected from a national registry, based on an observational prospective cohort of 30,737 live births after assisted reproductive technology (fresh embryo transfers: n = 20,932 and frozen embryo transfer [FET] n = 9805) between 2014 and 2015. A population of not-small for gestational age singletons conceived after fresh embryo transfers and FET, and their parents, was selected. Data on a number of variables were collected, including type of infertility, number of oocytes retrieved and vanishing twins. RESULTS: Preterm birth occurred in 7.7% (n = 1607) of fresh embryo transfers and 6.2% (n = 611) of frozen-thawed embryo transfers (P < 0.0001; adjusted odds ratio [aOR] = 1.34 [1.21-1.49]). Endometriosis and vanishing twin increased the risk of preterm birth after fresh embryo transfer (P < 0.001; aOR 1.32 and 1.78, respectively). Polycystic ovaries or more than 20 oocytes retrieved also increased preterm birth risk (aOR 1.31 and 1.30; P = 0.003 and P = 0.02, respectively); large oocyte cohort (>20) was no longer associated with the risk of prematurity in FET. CONCLUSION: Endometriosis remains a risk for prematurity even in the absence of intrauterine growth retardation, which suggests a dysimmune effect. Large oocyte cohorts obtained by stimulation, without clinical polycystic ovary syndrome diagnosed before attempts, do not affect FET outcomes, reinforcing the idea of a phenotypic difference in the clinical presentation of polycystic ovary syndrome.

Fetal growth disorders following medically assisted reproduction: due to maternal context or techniques? A national French cohort study.

RESEARCH QUESTION: What part do maternal context and medically assisted reproduction (MAR) techniques play in the risk of fetal growth disorders? DESIGN: This retrospective nationwide cohort study uses data available in the French National Health System database and focuses on the period from 2013 to 2017. Fetal growth disorders were divided into four groups according to the origin of pregnancy: fresh embryo transfer (n = 45,201), frozen embryo transfer (FET, n = 18,845), intrauterine insemination (IUI, n = 20,179) and natural conceptions (n = 3,412,868). Fetal growth disorders were defined from the percentiles of the weight distribution according to gestational age and sex: small and large for gestational age (SGA and LGA) if <10th and >90th percentiles, respectively. Analyses were performed using univariate and multivariate logistic models. RESULTS: Compared with births following natural conception, multivariate analysis showed that the risk of SGA was higher for births following fresh embryo transfer and IUI (adjusted odds ratio [aOR] 1.26 [1.22-1.29] and 1.08 [1.03-1.12], respectively) and significantly lower following FET (aOR 0.79 [0.75-0.83]). The risk of LGA was higher for births following FET (aOR 1.32 [1.27-1.38]), especially in artificial cycles when compared with ovulatory cycles (aOR 1.25 [1.15-1.36]). In the subgroup of births without any obstetrical or neonatal morbidity, the same increased risk of SGA and LGA were observed following fresh embryo transfer or IUI and FET (aOR 1.23 [1.19-1.27] or 1.06 [1.01-1.11] and aOR 1.36 [1.30-1.43], respectively). CONCLUSIONS: An effect of MAR techniques on the risks for SGA and LGA is suggested independently from maternal context and obstetrical or neonatal morbidities. Pathophysiological mechanisms remain poorly understood and should be further evaluated, as well as the influence of embryonic stage and freezing techniques.

A comparative methylome analysis reveals conservation and divergence of DNA methylation patterns and functions in vertebrates.

BACKGROUND: Cytosine DNA methylation is a heritable epigenetic mark present in most eukaryotic groups. While the patterns and functions of DNA methylation have been extensively studied in mouse and human, their conservation in other vertebrates remains poorly explored. In this study, we interrogated the distribution and function of DNA methylation in primary fibroblasts of seven vertebrate species including bio-medical models and livestock species (human, mouse, rabbit, dog, cow, pig, and chicken). RESULTS: Our data highlight both divergence and conservation of DNA methylation patterns and functions. We show that the chicken genome is hypomethylated compared to other vertebrates. Furthermore, compared to mouse, other species show a higher frequency of methylation of CpG-rich DNA. We reveal the conservation of large unmethylated valleys and patterns of DNA methylation associated with X-chromosome inactivation through vertebrate evolution and make predictions of conserved sets of imprinted genes across mammals. Finally, using chemical inhibition of DNA methylation, we show that the silencing of germline genes and endogenous retroviruses (ERVs) are conserved functions of DNA methylation in vertebrates. CONCLUSIONS: Our data highlight conserved properties of DNA methylation in vertebrate genomes but at the same time point to differences between mouse and other vertebrate species.

Overview of Gene Expression Dynamics during Human Oogenesis/Folliculogenesis.

The oocyte transcriptome follows a tightly controlled dynamic that leads the oocyte to grow and mature. This succession of distinct transcriptional states determines embryonic development prior to embryonic genome activation. However, these oocyte maternal mRNA regulatory events have yet to be decoded in humans. We reanalyzed human single-oocyte RNA-seq datasets previously published in the literature to decrypt the transcriptomic reshuffles ensuring that the oocyte is fully competent. We applied trajectory analysis (pseudotime) and a meta-analysis and uncovered the fundamental transcriptomic requirements of the oocyte at any moment of oogenesis until reaching the metaphase II stage (MII). We identified a bunch of genes showing significant variation in expression from primordial-to-antral follicle oocyte development and characterized their temporal regulation and their biological relevance. We also revealed the selective regulation of specific transcripts during the germinal vesicle-to-MII transition. Transcripts associated with energy production and mitochondrial functions were extensively downregulated, while those associated with cytoplasmic translation, histone modification, meiotic processes, and RNA processes were conserved. From the genes identified in this study, some appeared as sensitive to environmental factors such as maternal age, polycystic ovary syndrome, cryoconservation, and in vitro maturation. In the future, the atlas of transcriptomic changes described in this study will enable more precise identification of the transcripts responsible for follicular growth and oocyte maturation failures.

Does underlying infertility in natural conception modify the epigenetic control of imprinted genes and transposable elements in newborns?

RESEARCH QUESTION: Does the epigenetic control of imprinted genes and transposable elements at birth differ according to time to conception in natural conception and after intrauterine insemination (IUI)? DESIGN: A total of 144 singletons were included in four groups: 50 natural pregnancies obtained within 6 months after stopping contraception (group 1); 34 natural pregnancies with infertility period between 6 and 12 months (group 2); 36 pregnancies with an infertility period of more than 12 months (group 3) and 24 pregnancies obtained after IUI (group 4). RESULTS: The placental DNA methylation levels of H19/IGF2 and KCNQ1OT1 were lower in groups 2, 3 and 4 than in group 1 (P = 0.025 in the overall comparison). The DNA methylation rate for LINE-1 was higher in placentas from group 2 than in group 1 (P = 0.022). In cord blood, DNA methylation levels were not significantly different between groups except for H19/IGF2 for which the DNA methylation levels were higher in group 2 than in group 1 (H19/IGF2-seq1 and seq2: P = 0.023 and P = 0.002, respectively). In placenta tissue, compared with group 1, relative expression for SNRPN and for LINE-1 was significantly higher in group 2 (P = 0.002 and P < 0.001, respectively). The relative expression of KCNQ1 in placenta was lower in group 4 than in group 1 (P = 0.013). In cord blood, compared with group 1, the relative expression for H19 was significantly higher in group 3 (P = 0.026), and the relative expression of LINE-1 was higher in groups 2 and 3 and in group 4 (P < 0.001). CONCLUSIONS: Infertility itself, and not only ART techniques, could contribute to potential epigenetic risks for children.

Effect of paternal smoking on pre-implantation embryonic development: a prospective cohort study.

CONTEXT: Recent studies have failed to demonstrate the negative impact of male tobacco smoking on embryo development, raising the question of its actual implication on natural fecundity and assisted reproductive techniques outcomes. AIMS: To assess the impact of paternal smoking on embryo development. METHODS: In this prospective cohort study, 252 men from couples undergoing in vitro fertilisation (IVF) were included. Each patient was interviewed and took a carbon monoxide breath-test, creating three groups: non-smokers (n =113), former smokers (n =81) and active smokers (n =58). The Top-grade embryo ratio (primary endpoint), embryo morphokinetic parameters and clinical outcomes were assessed. KEY RESULTS: In a multivariate analyses based on 1521 embryos, no significant difference was found in the top-grade embryo ratio between the groups. Tobacco smoking had no impact on clinical outcomes. Compared to non-smokers the time to the pronuclei fading (tPNf, P =0.006) and the time to the first embryonic cleavage (t2, P =0.002) were shorter in smokers, and the t2 was also slightly shorter in former smokers (P =0.045). No other differences were found in the morphokinetic parameters. CONCLUSION: Even if a few differences were observed in the first timing of embryonic events, this study did not highlight a major embryonic and clinical impact of the paternal smoking status. IMPLICATION: The results obtained here are reassuring towards IVF outcomes. As maternal smoking is highly controlled in the IVF patients in this study, we speculate that the sperm selection process may limit the adverse effects of tobacco consumption on embryo development.

Analysis and quantification of female and male contributions to the first stages of embryonic kinetics: study from a time-lapse system.

PURPOSE: The few studies that examined the effect of male and/or female features on early embryo development, notably using the time-lapse system (TL), reported conflicting results. This can be explained by the small number of studies using an adapted model. METHODS: We used two original designs to study the female and male effects on embryo development: (1) based on embryos from donor oocytes (TL-DO), and (2) from donor sperm (TL-DS). Firstly, we analyzed the female and male similarities using an ad hoc intraclass correlation coefficient (ICC), then we completed the analysis with a multivariable model to assess the association between both male and female factors, and early embryo kinetics. A total of 572 mature oocytes (TL-DO: 293; TL-DS: 279), fertilized by intracytoplasmic sperm injection (ICSI) and incubated in a TL (Embryoscope®) were included from March 2013 to April 2019; 429 fertilized oocytes (TL-DO: 212; TL-DS: 217) were assessed. The timings of the first 48 h have been analyzed. RESULTS: The similarities in the timings thought to be related to the female component were significant: (ICC in both DO-DS designs respectively: tPB2: 9-18%; tPNa: 16-21%; tPNf: 40-26%; t2: 38-24%; t3: 15-20%; t4: 21-32%). Comparatively, those related to male were lower. Surprisingly after multivariable analyses, no intrinsic female factors were clearly identified. However, in TL-DO design, oligozoospermia was associated with a tendency to longer timings, notably for tPB2 (p = 0.026). CONCLUSION: This study quantifies the role of the oocyte in the first embryo cleavages, but without identified specific female factors. However, it also highlights that sperm may have an early embryonic effect.

The Gpr1/Zdbf2 locus provides new paradigms for transient and dynamic genomic imprinting in mammals.

Many loci maintain parent-of-origin DNA methylation only briefly after fertilization during mammalian development: Whether this form of transient genomic imprinting can impact the early embryonic transcriptome or even have life-long consequences on genome regulation and possibly phenotypes is currently unknown. Here, we report a maternal germline differentially methylated region (DMR) at the mouse Gpr1/Zdbf2 (DBF-type zinc finger-containing protein 2) locus, which controls the paternal-specific expression of long isoforms of Zdbf2 (Liz) in the early embryo. This DMR loses parental specificity by gain of DNA methylation at implantation in the embryo but is maintained in extraembryonic tissues. As a consequence of this transient, tissue-specific maternal imprinting, Liz expression is restricted to the pluripotent embryo, extraembryonic tissues, and pluripotent male germ cells. We found that Liz potentially functions as both Zdbf2-coding RNA and cis-regulatory RNA. Importantly, Liz-mediated events allow a switch from maternal to paternal imprinted DNA methylation and from Liz to canonical Zdbf2 promoter use during embryonic differentiation, which are stably maintained through somatic life and conserved in humans. The Gpr1/Zdbf2 locus lacks classical imprinting histone modifications, but analysis of mutant embryonic stem cells reveals fine-tuned regulation of Zdbf2 dosage through DNA and H3K27 methylation interplay. Together, our work underlines the developmental and evolutionary need to ensure proper Liz/Zdbf2 dosage as a driving force for dynamic genomic imprinting at the Gpr1/Zdbf2 locus.

Obstetrical outcomes and maternal morbidities associated with COVID-19 in pregnant women in France: A national retrospective cohort study.

BACKGROUND: To the best of our knowledge, no study has exhaustively evaluated the association between maternal morbidities and Coronavirus Disease 2019 (COVID-19) during the first wave of the pandemic in pregnant women. We investigated, in natural conceptions and assisted reproductive technique (ART) pregnancies, whether maternal morbidities were more frequent in pregnant women with COVID-19 diagnosis compared to pregnant women without COVID-19 diagnosis during the first wave of the COVID-19 pandemic. METHODS AND FINDINGS: We conducted a retrospective analysis of prospectively collected data in a national cohort of all hospitalizations for births ≥22 weeks of gestation in France from January to June 2020 using the French national hospitalization database (PMSI). Pregnant women with COVID-19 were identified if they had been recorded in the database using the ICD-10 (International Classification of Disease) code for presence of a hospitalization for COVID-19. A total of 244,645 births were included, of which 874 (0.36%) in the COVID-19 group. Maternal morbidities and adverse obstetrical outcomes among those with or without COVID-19 were analyzed with a multivariable logistic regression model adjusted on patient characteristics. Among pregnant women, older age (31.1 (±5.9) years old versus 30.5 (±5.4) years old, respectively, p < 0.001), obesity (0.7% versus 0.3%, respectively, p < 0.001), multiple pregnancy (0.7% versus 0.4%, respectively, p < 0.001), and history of hypertension (0.9% versus 0.3%, respectively, p < 0.001) were more frequent with COVID-19 diagnosis. Active smoking (0.2% versus 0.4%, respectively, p < 0.001) and primiparity (0.3% versus 0.4%, respectively, p < 0.03) were less frequent with COVID-19 diagnosis. Frequency of ART conception was not different between those with and without COVID-19 diagnosis (p = 0.28). When compared to the non-COVID-19 group, women in the COVID-19 group had a higher frequency of admission to ICU (5.9% versus 0.1%, p < 0.001), mortality (0.2% versus 0.005%, p < 0.001), preeclampsia/eclampsia (4.8% versus 2.2%, p < 0.001), gestational hypertension (2.3% versus 1.3%, p < 0.03), postpartum hemorrhage (10.0% versus 5.7%, p < 0.001), preterm birth at <37 weeks of gestation (16.7% versus 7.1%, p < 0.001), <32 weeks of gestation (2.2% versus 0.8%, p < 0.001), <28 weeks of gestation (2.4% versus 0.8%, p < 0.001), induced preterm birth (5.4% versus 1.4%, p < 0.001), spontaneous preterm birth (11.3% versus 5.7%, p < 0.001), fetal distress (33.0% versus 26.0%, p < 0.001), and cesarean section (33.0% versus 20.2%, p < 0.001). Rates of pregnancy terminations ≥22 weeks of gestation, stillbirths, gestational diabetes, placenta praevia, and placenta abruption were not significantly different between the COVID-19 and non-COVID-19 groups. The number of venous thromboembolic events was too low to perform statistical analysis. A limitation of this study relies in the possibility that asymptomatic infected women were not systematically detected. CONCLUSIONS: We observed an increased frequency of pregnant women with maternal morbidities and diagnosis of COVID-19 compared to pregnant women without COVID-19. It appears essential to be aware of this, notably in populations at known risk of developing a more severe form of infection or obstetrical morbidities and in order for obstetrical units to better inform pregnant women and provide the best care. Although causality cannot be determined from these associations, these results may be in line with recent recommendations in favor of vaccination for pregnant women.

Do in vitro fertilization, intrauterine insemination or female infertility impact the risk of congenital anomalies in singletons? A longitudinal national French study.

STUDY QUESTION: Do IVF, IUI or female infertility (i.e. endometriosis, polycystic ovary syndrome [PCOS] and primary ovarian insufficiency [POI]) lead to an increased risk of congenital anomalies in singletons? SUMMARY ANSWER: After multivariable adjustments, the increased risks of congenital defects associated with IUI were no longer significant, but the underlying maternal infertility presented a potential emental risk, in addition to the risk associated with IVF. WHAT IS KNOWN ALREADY: Most epidemiological studies suggest that singletons born from ART have a higher risk of birth defects, specifically musculoskeletal, cardiovascular and urogenital disorders. However, most of these studies were established on data obtained at birth or in the neonatal period and from relatively small populations or several registries. Moreover, to our knowledge, female infertility, which is a potential confounder, has never been included in the risk assessment. STUDY DESIGN, SIZE, DURATION: Using data from the French National Health System database, we conducted a comparative analysis of all singleton births (deliveries ≥22 weeks of gestation and/or >500 g of birthweight) in France over a 5-year period (2013-2017) resulting from fresh embryo or frozen embryo transfer (fresh-ET or FET from IVF/ICSI cycles), IUI and natural conception (NC). Data were available for this cohort of children at least up to early childhood (2.5 years old). PARTICIPANTS/MATERIALS, SETTING, METHODS: A total of 3 501 495 singleton births were included (3 417 089 from NC, 20 218 from IUI, 45 303 from fresh-ET and 18 885 from FET). Data were extracted from national health databases and used to identify major birth defects. Malformations were classified according to the 10th revision of the International Classification of Disease. To analyse the effect of mode of conception, multivariable analyses were performed with multiple logistic regression models adjusted for maternal age, primiparity, obesity, smoking, history of high blood pressure or diabetes and female infertility. MAIN RESULTS AND THE ROLE OF CHANCE: In our cohort of children, the overall prevalence of congenital malformations was 3.78% after NC, 4.53% after fresh-ET, 4.39% after FET and 3.91% after IUI (132 646 children with major malformations). Compared with infants conceived naturally, children born after fresh-ET and after FET had a significantly higher prevalence of malformations, with an adjusted odds ratio (aOR) of 1.15 [95% CI 1.10-1.20, P < 0.0001] and aOR of 1.13 [95% CI 1.05-1.21, P = 0.001], respectively. Among the 15 relevant subgroups of malformations studied, we observed a significantly increased risk of eight malformations in the fresh-ET group compared with the NC group (i.e. musculoskeletal, cardiac, urinary, digestive, neurological, cleft lip and/or palate and respiratory). In the FET group, this increased risk was observed for digestive and facial malformations. The overall risk of congenital malformations, and the risk by subtype, was similar in the IUI group and the NC group (overall risk: aOR of 1.01 [95% CI 0.94-1.08, P = 0.81]). In addition, there was an overall independent increase in the risk of congenital defects when the mothers were diagnosed with endometriosis (1.16 aOR [95% CI 1.10-1.22], P < 0.0001), PCOS (1.20 aOR [95% CI 1.08-1.34], P = 0.001) or POI (1.52 aOR [95% CI 1.23-1.88], P = 0.0001). Chromosomal, cardiac and neurological anomalies were more common in the three maternal infertility groups. LIMITATIONS, REASONS FOR CAUTION: Male infertility, the in vitro fertilization method (i.e. in vitro fertilization without or with sperm injection: conventional IVF vs ICSI) and embryo stage at transfer could not be taken into account. Furthermore, residual confounding cannot be excluded as well as uncertainties regarding the diagnostic criteria used for the three female infertilities. Findings for specific malformations should be interpreted with caution because the number of cases was small in some sub-groups (potentially due to the Type I error or multiple testing). WIDER IMPLICATIONS OF THE FINDINGS: In this large study, after multivariable maternal adjustments, a moderately increased risk of defects subsisted after IVF, while those associated with IUI were no longer significant. In addition, our results showed that underlying maternal infertility could contribute to the increased risk of defects associated with IVF. These novel findings highlight the importance of taking into account the ART treatment methods and the type of infertility. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the National Agency of Biomedicine. The authors have no competing interests to disclose. TRIAL REGISTRATION NUMBER: NA.

Endometriosis and assisted reproductive techniques independently related to mother-child morbidities: a French longitudinal national study.

RESEARCH QUESTION: Does endometriosis increase obstetric and neonatal complications, and does assisted reproductive technology (ART) cause additional risk of maternal or fetal morbidity? DESIGN: A nationwide cohort study (2013-2018) comparing maternal and perinatal morbidities in three groups of single pregnancies: spontaneous pregnancies without endometriosis; spontaneous pregnancies with endometriosis; and ART pregnancies in women with endometriosis. RESULTS: Mean maternal ages were 30.0 (SD = 5.3), 31.7 (SD = 4.8) and 33.1 years (SD = 4.0), for spontaneous conceptions, spontaneous conceptions with endometriosis and ART pregnancies with endometriosis groups, respectively (P < 0.0001). Comparison of spontaneous conceptions with endometriosis and spontaneous conceptions: endometriosis independently increased the risk of venous thrombosis (adjusted OR [aOR] 1.51, P < 0.001), pre-eclampsia (aOR 1.29, P < 0.001), placenta previa (aOR 2.62, P < 0.001), placental abruption (aOR 1.54, P < 0.001), premature birth (aOR 1.37, P < 0.001), small for gestational age (aOR 1.05, P < 0.001) and malformations (aOR 1.06, P = 0.049). Comparison of ART pregnancies with endometriosis and spontaneous conceptions with endometriosis: ART increased the risk of placenta previa (aOR 2.43, 95% CI 2.10 to 2.82, P < 0.001), premature birth (aOR 1.42, 95% CI 1.29 to 1.55, P < 0.001) and small for gestational age (aOR 1.18, 95% CI 1.10 to 1.27, P < 0.001), independently from the effect of endometriosis. Risk of pre-eclampsia, placental abruption or congenital malformations was not increased with ART. CONCLUSION: Endometriosis is an independent risk factor for mother and child morbidities. Maternal morbidity and perinatal morbidity were significantly increased by ART in addition to endometriosis; however, some perinatal and maternal morbidity risks were increasingly linked to pathologies related to infertility.

Vps13b is required for acrosome biogenesis through functions in Golgi dynamic and membrane trafficking.

The sperm acrosome is a lysosome-related organelle that develops using membrane trafficking from the Golgi apparatus as well as the endolysosomal compartment. How vesicular trafficking is regulated in spermatids to form the acrosome remains to be elucidated. VPS13B, a RAB6-interactor, was recently shown involved in endomembrane trafficking. Here, we report the generation of the first Vps13b-knockout mouse model and show that male mutant mice are infertile due to oligoasthenoteratozoospermia. This phenotype was explained by a failure of Vps13b deficient spermatids to form an acrosome. In wild-type spermatids, immunostaining of Vps13b and Rab6 revealed that they transiently locate to the acrosomal inner membrane. Spermatids lacking Vps13b did not present with the Golgi structure that characterizes wild-type spermatids and showed abnormal targeting of PNA- and Rab6-positive Golgi-derived vesicles to Eea1- and Lamp2-positive structures. Altogether, our results uncover a function of Vps13b in the regulation of the vesicular transport between Golgi apparatus, acrosome, and endolysosome.

Effects of assisted reproductive technologies on transposon regulation in the mouse pre-implanted embryo.

STUDY QUESTION: Do assisted reproductive technologies (ARTs) impact on the expression of transposable elements (TEs) in preimplantation embryos? SUMMARY ANSWER: The expression of all TE families is globally increased with mouse embryo culture with differences according to culture medium composition. WHAT IS KNOWN ALREADY: Mammalian genomes are subject to global epigenetic reprogramming during early embryogenesis. Whether ARTs could have consequences on this period of acute epigenetic sensitivity is the matter of intense research. So far, most studies have examined the impact of ARTs on the regulation of imprinted genes. However, very little attention has been given to the control of TEs, which exceed by far the number of genes and account for half of the mammalian genomic mass. This is of particular interest as TEs have the ability to modulate gene structure and expression, and show unique regulatory dynamics during the preimplantation period. STUDY DESIGN, SIZE, DURATION: Here, we evaluated for the first time the impact of ART procedures (superovulation, in-vitro fertilisation and embryo culture) on the control of different TE types throughout preimplantation development of mouse embryos. We also made use of a mouse model carrying a LINE-1 retrotransposition-reporter transgene to follow parental patterns of transmission and mobilisation. PARTICIPANTS/MATERIALS, SETTING, METHODS: Hybrid B6CBA/F1 mice were used for the expression analyses. Relative TE expression was evaluated by using the nCounter quantification methodology (Nanostring®). This quantitative method allowed us to simultaneously follow 15 TE targets. Another technique of quantification (RTqPCR) was also used.A mouse model carrying a LINE-1 retrotransposition-reporter transgene (LINE-1 GF21) was used to follow parental patterns of transmission and mobilisation. MAIN RESULTS AND THE ROLE OF CHANCE: We found that the superovulation step did not modify the dynamics nor the level of TE transcription across the preimplantation period. However, upon in-vitro culture, TE expression was globally increased at the blastocyst stage in comparison with in-vivo development. Finally, by monitoring the transmission and mobilisation of a transgenic LINE-1 transposon, we found that in-vitro fertilisation may alter the mendelian rate of paternal inheritance. LARGE SCALE DATA: N/A. LIMITATIONS, REASONS FOR CAUTION: Even though the Nanostring results concerning the dynamics of transcription throughout preimplantation development were based on pools of embryos originating from several females, only two pools were analysed per developmental stage. However, at the blastocyst stage, consistent expressional results were found between the Nanostring technology and the other technique of quantification used, RTqPCR. WIDER IMPLICATIONS OF THE FINDINGS: Our findings highlight the sensitivity of TEs to the ART environment and their great potential as biomarkers of culture medium-based effects. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by funding from the 'Agence de la Biomedecine', 'Conseil Régional de Bourgogne' and 'RCT grant from INSERM-DGOS'. The authors have no conflicts of interest to declare.

Placental volume and other first-trimester outcomes: are there differences between fresh embryo transfer, frozen-thawed embryo transfer and natural conception?

RESEARCH QUESTION: Does mode of conception influence placental volume and other first-trimester outcomes? DESIGN: This retrospective single-centre case-control study led in Dijon University Hospital included 252 singleton pregnancies (84 IVF with either fresh embryo transfer or frozen-thawed embryo transfer [FET] and 168 natural conceptions). First-trimester placental volume, uterine artery pulsatility index and maternal serum PAPP-A and beta-HCG were measured. Statistical analyses were adjusted for gestational age, the newborn's gender, maternal age, parity, body mass index and smoking status. RESULTS: Placental volume was significantly greater in the FET group than in the control group (P = 0.043) and fresh embryo transfer (P = 0.023) groups. At birth, fresh embryo transfer newborns were significantly smaller than controls (P = 0.01) and FET newborns (P = 0.008). Postpartum haemorrhage was far more frequent in FET than in controls and fresh embryo transfer group (38.1%, 2.6% and 1.9%, respectively; P < 0.0001). Placental volume positively correlated with PAPP-A, beta-HCG and the newborn's birth weight, and negatively correlated with uterine artery pulsatility index. CONCLUSIONS: Placental volume and other first-trimester parameters are modified by IVF with fresh embryo transfer and FET compared with natural conception, but with opposite trends. Given the different protocols used for these techniques, hormonal treatment per se may have a major effect on pregnancy outcomes through the modification of placental invasiveness.

[Cryoconservation of gametes: how to perform?] / Conservation des gamètes : quelles modalités ?

Cryoconservation of gametes : how to perform ? The patients can preserve their gametes when they are exposed to potential gonadotoxic pathology or treatment. In this context, the French bioethical law clearly states the obligation to inform the patients about the risks for their fertility and the possibilities to cryopreserve their gametes. Regional platforms of fertility preservation allow notably for the coordination of the oncology teams and the CECOS. For the men, sperm freezing is achieved by a slow and controlled temperature protocol. For the women, the oocytes are usually vitrified after hormonal stimulation and ovarian punction. For both, the gametes are cryopreserved in straws and stored in liquid nitrogen until use in assisted reproductive treatment (ART). Each year, the CECOS keeping the gametes interrogates patients on their wish to continue, or not, the cryoconservation. The gametes can only be used in ART by the patients only during their lifetime and with their consent, without alterations related to the duration of storage.

Conservation des gamètes : quelles modalités ? Les patient(e)s peuvent conserver leurs gamètes lorsqu'ils( ou elles) sont exposé(e)s à une pathologie ou un traitement potentiellement gonadotoxique. Dans ce contexte, la loi de bioéthique énonce très clairement l'obligation d'informer les patients des risques pour leur fertilité et des possibilités de conservation de leurs gamètes. Les plateformes régionales de préservation de la fertilité assurent la coordination entre les équipes d'oncologie et les centres d'étude et de conservation des oeufs et du sperme humains (CECOS) pour la mise en oeuvre de cette préservation. Pour les hommes, la congélation des spermatozoïdes est réalisée par une descente en température lente et contrôlée. Pour les femmes, la cryoconservation des ovocytes se fait par vitrification après stimulation hormonale et ponction ovarienne. Dans les deux cas, les gamètes sont conservés dans des paillettes qui sont stockées dans une cuve d'azote liquide jusqu'à utilisation en assistance médicale à la procréation (AMP). Le CECOS conservant les gamètes interroge chaque année par courrier les patients concernés sur leur souhait de poursuivre, ou non, la cryoconservation. Les gamètes pourront être utilisés en AMP par les patients de leur vivant et après leur consentement, sans altération liée à la durée de stockage.

Germline correction of an epimutation related to Silver-Russell syndrome.

Like genetic mutations, DNA methylation anomalies or epimutations can disrupt gene expression and lead to human diseases. However, unlike genetic mutations, epimutations can in theory be reverted through developmental epigenetic reprograming, which should limit their transmission across generations. Following the request for a parental project of a patient diagnosed with Silver-Russell syndrome (SRS), and the availability of both somatic and spermatozoa DNA from the proband and his father, we had the exceptional opportunity to evaluate the question of inheritance of an epimutation. We provide here for the first time evidence for efficient reversion of a constitutive epimutation in the spermatozoa of an SRS patient, which has important implication for genetic counseling.

Eutherian mammals use diverse strategies to initiate X-chromosome inactivation during development.

X-chromosome inactivation (XCI) in female mammals allows dosage compensation for X-linked gene products between the sexes. The developmental regulation of this process has been extensively investigated in mice, where the X chromosome of paternal origin (Xp) is silenced during early embryogenesis owing to imprinted expression of the regulatory RNA, Xist (X-inactive specific transcript). Paternal XCI is reversed in the inner cell mass of the blastocyst and random XCI subsequently occurs in epiblast cells. Here we show that other eutherian mammals have very different strategies for initiating XCI. In rabbits and humans, the Xist homologue is not subject to imprinting and XCI begins later than in mice. Furthermore, Xist is upregulated on both X chromosomes in a high proportion of rabbit and human embryo cells, even in the inner cell mass. In rabbits, this triggers XCI on both X chromosomes in some cells. In humans, chromosome-wide XCI has not initiated even by the blastocyst stage, despite the upregulation of XIST. The choice of which X chromosome will finally become inactive thus occurs downstream of Xist upregulation in both rabbits and humans, unlike in mice. Our study demonstrates the remarkable diversity in XCI regulation and highlights differences between mammals in their requirement for dosage compensation during early embryogenesis.

Plasticity in Dnmt3L-dependent and -independent modes of de novo methylation in the developing mouse embryo.

A stimulatory DNA methyltransferase co-factor, Dnmt3L, has evolved in mammals to assist the process of de novo methylation, as genetically demonstrated in the germline. The function of Dnmt3L in the early embryo remains unresolved. By combining developmental and genetic approaches, we find that mouse embryos begin development with a maternal store of Dnmt3L, which is rapidly degraded and does not participate in embryonic de novo methylation. A zygotic-specific promoter of Dnmt3l is activated following gametic methylation loss and the potential recruitment of pluripotency factors just before implantation. Importantly, we find that zygotic Dnmt3L deficiency slows down the rate of de novo methylation in the embryo by affecting methylation density at some, but not all, genomic sequences. Dnmt3L is not strictly required, however, as methylation patterns are eventually established in its absence, in the context of increased Dnmt3A protein availability. This study proves that the postimplantation embryo is more plastic than the germline in terms of DNA methylation mechanistic choices and, importantly, that de novo methylation can be achieved in vivo without Dnmt3L.

CFTR p.Arg117His associated with CBAVD and other CFTR-related disorders.

BACKGROUND: The high frequency of the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene mutation p.Arg117His in patients with congenital bilateral absence of the vas deferens (CBAVD) and in newborns screened for CF has created a dilemma. METHODS: Phenotypic and genotypic data were retrospectively collected in 179 non-newborn French individuals carrying p.Arg117His and a second CFTR mutation referred for symptoms or family history, by all French molecular genetics laboratories, referring physicians, CF care centres and infertility clinics. RESULTS: 97% of the patients had the intronic T7 normal variant in cis with p.Arg117His. 89% patients were male, with CBAVD being the reason for referral in 76%. In 166/179 patients with available detailed clinical features, final diagnoses were: four late-onset marked pulmonary disease, 83 isolated CBAVD, 67 other CFTR-related phenotypes, including 44 CBAVD with pulmonary and/or pancreatic symptoms and 12 asymptomatic cases. Respiratory symptoms were observed in 30% of the patients, but the overall phenotype was mild. No correlation was observed between sweat chloride concentrations and disease severity. Five couples at risk of CF offspring were identified and four benefited from prenatal or preimplantation genetic diagnoses (PND or PGD). Eight children were born, including four who were compound heterozygous for p.Arg117His and one with a severe CF mutation. CONCLUSIONS: Patients with CBAVD carrying p.Arg117His and a severe CF mutation should benefit from a clinical evaluation and follow-up. Depending on the CBAVD patients' genotype, a CFTR analysis should be considered in their partners in order to identify CF carrier couples and offer PND or PGD.