Human embryo live imaging reveals nuclear DNA shedding during blastocyst expansion and biopsy.

Proper preimplantation development is essential to assemble a blastocyst capable of implantation. Live imaging has uncovered major events driving early development in mouse embryos; yet, studies in humans have been limited by restrictions on genetic manipulation and lack of imaging approaches. We have overcome this barrier by combining fluorescent dyes with live imaging to reveal the dynamics of chromosome segregation, compaction, polarization, blastocyst formation, and hatching in the human embryo. We also show that blastocyst expansion mechanically constrains trophectoderm cells, causing nuclear budding and DNA shedding into the cytoplasm. Furthermore, cells with lower perinuclear keratin levels are more prone to undergo DNA loss. Moreover, applying trophectoderm biopsy, a mechanical procedure performed clinically for genetic testing, increases DNA shedding. Thus, our work reveals distinct processes underlying human development compared with mouse and suggests that aneuploidies in human embryos may not only originate from chromosome segregation errors during mitosis but also from nuclear DNA shedding.

Intra-patient analysis of individual weight gain or loss between IVF cycles: cycle now and transfer later.

STUDY QUESTION: What is the impact of clinically significant weight change on outcomes related to IVF cycle performance? SUMMARY ANSWER: While individual weight loss did not significantly impact ovarian response to stimulation or other cycle outcome parameters in our study, some positive associations were found for individual weight gain. WHAT IS KNOWN ALREADY: The role of weight-change in patients undergoing IVF has been largely studied by comparing weight loss in different cohorts of patients stratified by a static BMI. Specifically, obesity has been extensively studied in relation to its negative effects on assisted or unassisted conception outcomes and ovulatory function. Previous research has shown conflicting results, while BMI, which is commonly used as a marker of obesity, may not accurately reflect the underlying factors affecting fertility in obese patients. STUDY DESIGN, SIZE, DURATION: This study utilized a retrospective within-patient repeated measurement analysis design to assess the impact of weight change on IVF outcomes in cycles where all embryos were cryopreserved at the blastocyst stage for transfer at a later date. PARTICIPANTS/MATERIALS, SETTING, METHODS: The study was conducted at an academically affiliated fertility center. The data included 961 women who underwent at least two IVF cycles between December 2014 and June 2020, with documented short-term weight gain (n = 607) or weight loss (n = 354) within 1 year from their initial IVF cycle. Multivariable generalized estimating equations (GEE) and generalized linear mixed models (GLMM) were employed to assess associations between weight change and outcomes across cycles. MAIN RESULTS AND THE ROLE OF CHANCE: The multivariable models indicated that weight loss did not show any significant associations with the numbers of oocytes retrieved, or mature oocytes, the fertilization rate or the blastulation rate. However, weight gain demonstrated a minor positive association with the number of oocytes retrieved in both GEE models (coefficient: 0.01, 95% CI: 0.00-0.01) and GLMM models (0.01, 95% CI: 0.01-0.00). There was also a potential increase in the fertilization rate with weight gain, as indicated by a positive coefficient in both GEE models (coefficient: 0.01, 95% CI: 0.00-0.02) and GLMM models (coefficient: 0.01, 95% CI: 0.00-0.01). However, the association between weight gain and the embryo blastulation rate was not statistically significant in any model. LIMITATIONS, REASONS FOR CAUTION: This study focused on cycle performance parameters instead of reproductive outcomes, which restricted our ability to evaluate the impact of weight change on cumulative live birth rates. Additionally, the study did not account for variables such as stimulation protocols, potentially introducing confounding factors and limiting the generalizability of the results. WIDER IMPLICATIONS OF THE FINDINGS: Although obesity is associated with adverse obstetrical risks, there is less evidence of adverse reproductive outcomes in IVF cycles. We therefore recommend that an IVF cycle should not be delayed due to weight, so that the patient is not adversely affected by increasing age. The IVF cycle should aim to freeze all embryos, so that embryo transfer can then occur after weight loss, so as to limit the recognized obstetrical risks. STUDY FUNDING/COMPETING INTEREST(S): The study was not funded and there were no competing interests. TRIAL REGISTRATION NUMBER: N/A.

Do sperm factors influence embryonic aneuploidy? Long live the oocyte.

STUDY QUESTION: What is the impact of male age- and sperm-related factors on embryonic aneuploidy? SUMMARY ANSWER: Using a 3-fold analysis framework encompassing patient-level, embryo-level, and matching analysis, we found no clinically significant interactions between male age and sperm quality with embryo ploidy. WHAT IS KNOWN ALREADY: While the effect of maternal age on embryo chromosomal aneuploidy is well-established, the impact of male age and sperm quality on ploidy is less well-defined. STUDY DESIGN, SIZE, DURATION: This retrospective cohort study analyzed autologous preimplantation genetic testing for aneuploidy (PGT-A) and frozen embryo transfer cycles from December 2014 to June 2021. The study involved 11 087 cycles from 8484 patients, with a total of 35 797 embryos. PARTICIPANTS/MATERIALS, SETTING, METHODS: The aneuploidy rate, calculated as the ratio of aneuploid blastocysts to the total number of blastocysts biopsied in a single treatment cycle, was evaluated. In the embryo-level analysis, the main outcome measure was the ploidy state of the embryos. The study employed a multifaceted analytical approach that included a patient-level analysis using generalized linear mixed models, an embryo-level analysis focusing on chromosomal ploidy, and a propensity score matching analysis contrasting groups with distinct ploidy rates (0% and 100%). There were no interventions as this was an observational study of PGT-A cycles. MAIN RESULTS AND THE ROLE OF CHANCE: No clinically relevant factors influencing ploidy rate related to male and sperm quality were revealed. In contrast, female age (coefficient = -0.053), BMI (coefficient = 0.003), prior ART cycle (coefficient = -0.066), and number of oocytes retrieved (coefficient = -0.018) were identified at the patient level. Embryo analysis identified age (coefficient = -0.1244) and ICSI usage (coefficient = -0.0129) as significant factors. Despite these, no significant interactions between male and female assessed factors on the ploidy rate emerged. Propensity score matching between maximal (100% vs 0%) euploid rates did not reveal significant differences of influence by male age and sperm quality. LIMITATIONS, REASONS FOR CAUTION: The focus on patients having blastocyst biopsy for PGT-A may not reflect the broader IVF population. Other semen quality parameters like DNA fragmentation were not included. Exclusion of embryo mosaicism from the analysis could affect aneuploidy rate interpretations. There may also be unmeasured influences like lifestyle or environmental factors. WIDER IMPLICATIONS OF THE FINDINGS: Male age and sperm quality parameters were consistent across both maximal and minimal ploidy rate comparisons. No significant clinical characteristics related to the factors assessed for the male-influenced blastocyst ploidy status, confirming the dominancy of the oocyte and female age. STUDY FUNDING/COMPETING INTEREST(S): The study was not funded. There are no competing interests. TRIAL REGISTRATION NUMBER: N/A.

Metabolic imaging of human embryos is predictive of ploidy status but is not associated with clinical pregnancy outcomes: a pilot trial.

STUDY QUESTION: Does fluorescence lifetime imaging microscopy (FLIM)-based metabolic imaging assessment of human blastocysts prior to frozen transfer correlate with pregnancy outcomes? SUMMARY ANSWER: FLIM failed to distinguish consistent patterns in mitochondrial metabolism between blastocysts leading to pregnancy compared to those that did not. WHAT IS KNOWN ALREADY: FLIM measurements provide quantitative information on NAD(P)H and flavin adenine dinucleotide (FAD+) concentrations. The metabolism of embryos has long been linked to their viability, suggesting the potential utility of metabolic measurements to aid in selection. STUDY DESIGN, SIZE, DURATION: This was a pilot trial enrolling 121 IVF couples who consented to have their frozen blastocyst measured using non-invasive metabolic imaging. After being warmed, 105 couples' good-quality blastocysts underwent a 6-min scan in a controlled temperature and gas environment. FLIM-assessed blastocysts were then transferred without any intervention in management. PARTICIPANTS/MATERIALS, SETTING, METHODS: Eight metabolic parameters were obtained from each blastocyst (4 for NAD(P)H and 4 for FAD): short and long fluorescence lifetime, fluorescence intensity, and fraction of the molecule engaged with enzyme. The redox ratio (intensity of NAD(P)H)/(intensity of FAD) was also calculated. FLIM data were combined with known metadata and analyzed to quantify the ability of metabolic imaging to differentiate embryos that resulted in pregnancy from embryos that did not. De-identified discarded aneuploid human embryos (n = 158) were also measured to quantify correlations with ploidy status and other factors. Statistical comparisons were performed using logistic regression and receiver operating characteristic (ROC) curves with 5-fold cross-validation averaged over 100 repeats with random sampling. AUC values were used to quantify the ability to distinguish between classes. MAIN RESULTS AND THE ROLE OF CHANCE: No metabolic imaging parameters showed significant differences between good-quality blastocysts resulting in pregnancy versus those that did not. A logistic regression using metabolic data and metadata produced an ROC AUC of 0.58. In contrast, robust AUCs were obtained when classifying other factors such as comparison of Day 5 (n = 64) versus Day 6 (n = 41) blastocysts (AUC = 0.78), inner cell mass versus trophectoderm (n = 105: AUC = 0.88) and aneuploid (n = 158) versus euploid and positive pregnancy embryos (n = 108) (AUC = 0.82). LIMITATIONS, REASONS FOR CAUTION: The study protocol did not select which embryo to transfer and the cohort of 105 included blastocysts were all high quality. The study was also limited in number of participants and study sites. Increased power and performing the trial in more sites may have provided a stronger conclusion regarding the merits of the use of FLIM clinically. WIDER IMPLICATIONS OF THE FINDINGS: FLIM failed to distinguish consistent patterns in mitochondrial metabolism between good-quality blastocysts leading to pregnancy compared to those that did not. Blastocyst ploidy status was, however, highly distinguishable. In addition, embryo regions and embryo day were consistently revealed by FLIM. While metabolic imaging detects mitochondrial metabolic features in human blastocysts, this pilot trial indicates it does not have the potential to serve as an effective embryo viability detection tool. This may be because mitochondrial metabolism plays an alternative role post-implantation. STUDY FUNDING/COMPETING INTEREST(S): This study was sponsored by Optiva Fertility, Inc. Boston IVF contributed to the clinical site and services. Becker Hickl, GmbH, provided the FLIM system on loan. T.S. was the founder and held stock in Optiva Fertility, Inc., and D.S. and E.S. had options with Optiva Fertility, Inc., during this study. TRIAL REGISTRATION NUMBER: The study was approved by WCG Connexus IRB (Study Number 1298156).

The impact of implementing a non-invasive preimplantation genetic testing for aneuploidies (niPGT-A) embryo culture protocol on embryo viability and clinical outcomes.

STUDY QUESTION: Are modifications in the embryo culture protocol needed to perform non-invasive preimplantation genetic testing for aneuploidies (niPGT-A) affecting clinical reproductive outcomes, including blastocyst development and pregnancy outcomes? SUMMARY ANSWER: The implementation of an embryo culture protocol to accommodate niPGT-A has no impact on blastocyst viability or pregnancy outcomes. WHAT IS KNOWN ALREADY: The recent identification of embryo cell-free (cf) DNA in spent blastocyst media has created the possibility of simplifying PGT-A. Concerns, however, have arisen at two levels. First, the representativeness of that cfDNA to the real ploidy status of the embryo. Second, the logistical changes that need to be implemented by the IVF laboratory when performing niPGT-A and their effect on reproductive outcomes. Concordance rates of niPGT-A to invasive PGT-A have gradually improved; however, the impact of culture protocol changes is not as well understood. STUDY DESIGN, SIZE, DURATION: As part of a trial examining concordance rates of niPGT-A versus invasive PGT-A, the IVF clinics implemented a specific niPGT-A embryo culture protocol. Briefly, this involved initial culture of fertilized oocytes following each laboratory standard routine up to Day 4. On Day 4, embryos were washed and cultured individually in 10 µl of fresh media. On Day 6 or 7, blastocysts were then biopsied, vitrified, and media collected for the niPGT-A analysis. Six IVF clinics from the previously mentioned trial were enrolled in this analysis. In the concordance trial, Clinic A cultured all embryos (97 cycles and 355 embryos) up to Day 6 or 7, whereas in the remaining clinics (B-F) (379 cycles), nearly a quarter of all the blastocysts (231/985: 23.5%) were biopsied on Day 5, with the remaining blastocysts following the niPGT-A protocol (754/985: 76.5%). During the same period (April 2018-December 2020), the IVF clinics also performed standard invasive PGT-A, which involved culture of embryos up to Days 5, 6, or 7 when blastocysts were biopsied and vitrified. PARTICIPANTS/MATERIALS, SETTING, METHODS: In total, 428 (476 cycles) patients were in the niPGT-A study group. Embryos from 1392 patients underwent the standard PGT-A culture protocol and formed the control group. Clinical information was obtained and analyzed from all the patients. Statistical comparisons were performed between the study and the control groups according to the day of biopsy. MAIN RESULTS AND THE ROLE OF CHANCE: The mean age, number of oocytes, fertilization rates, and number of blastocysts biopsied were not significantly different for the study and the control group. Regarding the overall pregnancy outcomes, no significant effect was observed on clinical pregnancy rate, miscarriage rate, or ongoing pregnancy rate (≥12 weeks) in the study group compared to the control group when stratified by day of biopsy. LIMITATIONS, REASONS FOR CAUTION: The limitations are intrinsic to the retrospective nature of the study, and to the fact that the study was conducted in invasive PGT-A patients and not specifically using niPGT-A cases. WIDER IMPLICATIONS OF THE FINDINGS: This study shows that modifying current IVF laboratory protocols to adopt niPGT-A has no impact on the number of blastocysts available for transfer and overall clinical outcomes of transferred embryos. Whether removal of the invasive biopsy step leads to further improvements in pregnancy rates awaits further studies. STUDY FUNDING/COMPETING INTEREST(S): This study was funded by Igenomix. C.R., L.N.-S., and D.V. are employees of Igenomix. D.S. was on the Scientific Advisory Board of Igenomix during the study. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov (NCT03520933).

Implicit bias in diagnosing mosaicism amongst preimplantation genetic testing providers: results from a multicenter study of 36 395 blastocysts.

STUDY QUESTION: Does the diagnosis of mosaicism affect ploidy rates across different providers offering preimplantation genetic testing for aneuploidies (PGT-A)? SUMMARY ANSWER: Our analysis of 36 395 blastocyst biopsies across eight genetic testing laboratories revealed that euploidy rates were significantly higher in providers reporting low rates of mosaicism. WHAT IS KNOWN ALREADY: Diagnoses consistent with chromosomal mosaicism have emerged as a third category of possible embryo ploidy outcomes following PGT-A. However, in the era of mosaicism, embryo selection has become increasingly complex. Biological, technical, analytical, and clinical complexities in interpreting such results have led to substantial variability in mosaicism rates across PGT-A providers and clinics. Critically, it remains unknown whether these differences impact the number of euploid embryos available for transfer. Ultimately, this may significantly affect clinical outcomes, with important implications for PGT-A patients. STUDY DESIGN, SIZE, DURATION: In this international, multicenter cohort study, we reviewed 36 395 consecutive PGT-A results, obtained from 10 035 patients across 11 867 treatment cycles, conducted between October 2015 and October 2021. A total of 17 IVF centers, across eight PGT-A providers, five countries and three continents participated in the study. All blastocysts were tested using trophectoderm biopsy and next-generation sequencing. Both autologous and donation cycles were assessed. Cycles using preimplantation genetic testing for structural rearrangements were excluded from the analysis. PARTICIPANTS/MATERIALS, SETTING, METHODS: The PGT-A providers were randomly categorized (A to H). Providers B, C, D, E, F, G, and H all reported mosaicism, whereas Provider A reported embryos as either euploid or aneuploid. Ploidy rates were analyzed using multilevel mixed linear regression. Analyses were adjusted for maternal age, paternal age, oocyte source, number of embryos biopsied, day of biopsy, and PGT-A provider, as appropriate. We compared associations between genetic testing providers and PGT-A outcomes, including the number of chromosomally normal (euploid) embryos determined to be suitable for transfer. MAIN RESULTS AND THE ROLE OF CHANCE: The mean maternal age (±SD) across all providers was 36.2 (±5.2). Our findings reveal a strong association between PGT-A provider and the diagnosis of euploidy and mosaicism. Amongst the seven providers that reported mosaicism, the rates varied from 3.1% to 25.0%. After adjusting for confounders, we observed a significant difference in the likelihood of diagnosing mosaicism across providers (P < 0.001), ranging from 6.5% (95% CI: 5.2-7.4%) for Provider B to 35.6% (95% CI: 32.6-38.7%) for Provider E. Notably, adjusted euploidy rates were highest for providers that reported the lowest rates of mosaicism (Provider B: euploidy, 55.7% (95% CI: 54.1-57.4%), mosaicism, 6.5% (95% CI: 5.2-7.4%); Provider H: euploidy, 44.5% (95% CI: 43.6-45.4%), mosaicism, 9.9% (95% CI: 9.2-10.6%)); and Provider D: euploidy, 43.8% (95% CI: 39.2-48.4%), mosaicism, 11.0% (95% CI: 7.5-14.5%)). Moreover, the overall chance of having at least one euploid blastocyst available for transfer was significantly higher when mosaicism was not reported, when we compared Provider A to all other providers (OR = 1.30, 95% CI: 1.13-1.50). Differences in diagnosing and interpreting mosaic results across PGT-A laboratories raise further concerns regarding the accuracy and relevance of mosaicism predictions. While we confirmed equivalent clinical outcomes following the transfer of mosaic and euploid blastocysts, we found that a significant proportion of mosaic embryos are not used for IVF treatment. LIMITATIONS, REASONS FOR CAUTION: Due to the retrospective nature of the study, associations can be ascertained, however, causality cannot be established. Certain parameters such as blastocyst grade were not available in the dataset. Furthermore, certain platform-related and clinic-specific factors may not be readily quantifiable or explicitly captured in our dataset. As such, a full elucidation of all potential confounders accounting for variability may not be possible. WIDER IMPLICATIONS OF THE FINDINGS: Our findings highlight the strong need for standardization and quality assurance in the industry. The decision not to transfer mosaic embryos may ultimately reduce the chance of success of a PGT-A cycle by limiting the pool of available embryos. Until we can be certain that mosaic diagnoses accurately reflect biological variability, reporting mosaicism warrants utmost caution. A prudent approach is imperative, as it may determine the difference between success or failure for some patients. STUDY FUNDING/COMPETING INTEREST(S): This work was supported by the Torres Quevedo Grant, awarded to M.P. (PTQ2019-010494) by the Spanish State Research Agency, Ministry of Science and Innovation, Spain. M.P., L.B., A.R.L., A.L.R.d.C.L., N.P.P., M.P., D.S., F.A., A.P., B.M., L.D., F.V.M., D.S., M.R., E.P.d.l.B., A.R., and R.V. have no competing interests to declare. B.L., R.M., and J.A.O. are full time employees of IB Biotech, the genetics company of the Instituto Bernabeu group, which performs preimplantation genetic testing. M.G. is a full time employee of Novagen, the genetics company of Cegyr, which performs preimplantation genetic testing. TRIAL REGISTRATION NUMBER: N/A.

Perinatal outcomes are similar in programmed and modified natural frozen embryo transfer cycles.

RESEARCH QUESTION: How do perinatal outcomes differ between programmed and modified natural frozen embryo transfer (FET) cycles? DESIGN: A retrospective cohort study of 839 patients was undertaken at a university-affiliated fertility practice undergoing single blastocyst FET cycles between 2014 and 2020. The primary outcome measures were the incidence of ischaemic placental disease, small for gestational age (SGA), intrauterine growth restriction (IUGR), preterm delivery, birth weight, and mode of delivery. RESULTS: When comparing programmed FET cycles with modified natural FET cycles, there was no increased risk of ischaemic placental disease [adjusted risk ratio (aRR) 0.83, 95% CI 0.61-1.14], IUGR (unadjusted RR 0.50, 95% CI 0.14-1.77), preterm delivery (aRR 1.11, 95% CI 0.72-1.70) or SGA (aRR 0.69, 95% CI 0.40-1.19). Patients in the programmed cohort had increased risk of caesarean delivery (aRR 1.32, 95% CI 1.10-1.59). These outcomes were unchanged when limited to patients undergoing their first FET cycle. CONCLUSIONS: There are no differences in patient and neonatal clinical outcomes between programmed and modified natural FET cycles. The choice of FET protocol should remain a shared decision between patient and provider.

Effort in manual operation of reproductive health cryostorage facilities.

RESEARCH QUESTION: What areas of manual IVF cryostorage operations are common to the safe operation of IVF cryostorage facilities and require effort from embryologists? DESIGN: Observational time and motion data were collected by two observers equipped with the digital cameras over 2 weeks at four well-characterized US IVF centres (sites α, ß, γ and δ) from 12 participants performing cryostorage tasks. To understand the work processes of the different sites and assist in the data analysis, informal interviews were conducted with the study participants and laboratory directors. Data were analysed to identify work processes that might be eliminated or diminished by automation and software improvements. RESULTS: On average, it took 3.4 data record queries per retrieval from cryostorage to identify a cane, while the canister was lifted an average of 1.5 times per retrieval, with a mean 11.8 ± 9.2 s per lift. Of the total time spent working with cryostorage equipment, 47.25% was of a fatiguing nature. Sites α, ß and γ utilized one person to fill the liquid nitrogen storage Dewars, while site δ had two technicians working in tandem to move and fill the Dewars, with different frequencies and determination factors for refills and efficiencies. CONCLUSIONS: This time and motion study demonstrated significant time investment, task redundancy and fatiguing working conditions among embryologists using manual cryostorage processes. There was a disparity of processes and space capacity across different laboratories. Some of these issues may be addressed by the integration of automation and technology solutions.

Effect of time post warming to embryo transfer on human blastocyst metabolism and pregnancy outcome.

PURPOSE: This study is aiming to test whether variation in post warming culture time impacts blastocyst metabolism or pregnancy outcome. METHODS: In this single center retrospective cohort study, outcomes of 11,520 single frozen embryo transfer (FET) cycles were analyzed from January 2015 to December 2020. Patient treatments included both natural and programmed cycles. Time categories were determined using the time between blastocyst warming and embryo transfer: 0 (0- <1h), 1 (1-<2h), 2 (2-<3h), 3(3-<4h), 4 (4-<5), 5 (5-<6), 6 (6-<7) and 7 (7-8h). Non-invasive metabolic imaging of discarded human blastocysts for up to 10h was also performed using Fluorescence lifetime imaging microscopy (FLIM) to examine for metabolic perturbations during culture. RESULTS: The mean age of patients across all time categories were comparable (35.6 ± 3.9). Live birth rates (38-52%) and miscarriage rate (5-11%) were not statistically different across post-warming culture time. When assessing pregnancy outcomes based on the use of PGT-A, miscarriage and live birth rates were not statistically different across culture hours in both PGT-A and non-PGT cycles. Further metabolic analysis of blastocysts for the duration of 10h of culture post warming, revealed minimal metabolic changes of embryos in culture. CONCLUSION: Overall, our results show that differences in the time of post warming culture have no significant impact on miscarriage or live birth rate for frozen embryo transfers. This information can be beneficial for clinical practices with either minimal staffing or a high number of patient cases.

Sperm selection by the oviduct: perspectives for male fertility and assisted reproductive technologies†.

The contribution of sperm to embryogenesis is gaining attention with up to 50% of infertility cases being attributed to a paternal factor. The traditional methods used in assisted reproductive technologies for selecting and assessing sperm quality are mainly based on motility and viability parameters. However, other sperm characteristics, including deoxyribonucleic acid integrity, have major consequences for successful live birth. In natural reproduction, sperm navigate the male and female reproductive tract to reach and fertilize the egg. During transport, sperm encounter many obstacles that dramatically reduce the number arriving at the fertilization site. In humans, the number of sperm is reduced from tens of millions in the ejaculate to hundreds in the Fallopian tube (oviduct). Whether this sperm population has higher fertilization potential is not fully understood, but several studies in animals indicate that many defective sperm do not advance to the site of fertilization. Moreover, the oviduct plays a key role in fertility by modulating sperm transport, viability, and maturation, providing sperm that are ready to fertilize at the appropriate time. Here we present evidence of sperm selection by the oviduct with emphasis on the mechanisms of selection and the sperm characteristics selected. Considering the sperm parameters that are essential for healthy embryonic development, we discuss the use of novel in vitro sperm selection methods that mimic physiological conditions. We propose that insight gained from understanding how the oviduct selects sperm can be translated to assisted reproductive technologies to yield high fertilization, embryonic development, and pregnancy rates.

Noninvasive metabolic profiling of cumulus cells, oocytes, and embryos via fluorescence lifetime imaging microscopy: a mini-review.

A major challenge in ART is to select high-quality oocytes and embryos. The metabolism of oocytes and embryos has long been linked to their viability, suggesting the potential utility of metabolic measurements to aid in selection. Here, we review recent work on noninvasive metabolic imaging of cumulus cells, oocytes, and embryos. We focus our discussion on fluorescence lifetime imaging microscopy (FLIM) of the autofluorescent coenzymes NAD(P)H and flavine adenine dinucleotide (FAD+), which play central roles in many metabolic pathways. FLIM measurements provide quantitative information on NAD(P)H and FAD+ concentrations and engagement with enzymes, leading to a robust means of characterizing the metabolic state of cells. We argue that FLIM is a promising approach to aid in oocyte and embryo selection.

Day after rescue ICSI: eliminating total fertilization failure after conventional IVF with high live birth rates following cryopreserved blastocyst transfer.

STUDY QUESTION: What is the impact of day after rescue ICSI (r-ICSI) on success of fresh and frozen embryo transfers? SUMMARY ANSWER: The use of r-ICSI can virtually allay fears of total fertilization failure (TFF) after conventional IVF (C-IVF) and achieve high live birth rates after frozen blastocyst transfer. WHAT IS KNOWN ALREADY: More infertility clinics have resorted to the use of ICSI in place of C-IVF in IVF treatment owing to fear of TFF or a low fertilization rate. r-ICSI has been attempted either on the day of IVF or the day after. Day after r-ICSI has proved unsuccessful in the past. STUDY DESIGN, SIZE, DURATION: A retrospective data analysis was performed of 16 608 qualifying cases between April 2010 and July 2021 conducted at a single private academically affiliated fertility clinic. PARTICIPANTS/MATERIALS, SETTING, METHODS: r-ICSI was performed principally on patients with >4 metaphase II oocytes, showing no signs of fertilization 18 h after C-IVF. C-IVF was performed on patients who had >4 million total motile sperm after preparation. r-ICSI was then performed 18-24 h after insemination, using the sperm sample from the previous day. r-ICSI fertilization rates, cryopreservation of cleavage and blastocysts embryos, and pregnancy rates after fresh or frozen transfer were then assessed. MAIN RESULTS AND THE ROLE OF CHANCE: r-ICSI was performed on 377 patients (2.3% of eligible retrieval cycles) who had a mean (±SD) female and male age of 35.9 ± 4.5 and 38.1 ± 9.1 years, respectively. A total of 5459 oocytes were initially retrieved. Of the oocytes undergoing r-ICSI, 2389 (49.5%) fertilized normally, and 205 (54.4%) patients underwent a fresh embryo transfer. The live birth rates were 23/186 (12.3%) for fresh cleavage and 5/19 (26.3%) for fresh blastocyst stage transfers. In 145 cycles a blastocyst was frozen, and 137 transfers were performed with a 64/137 (46.7%) live birth rate. Of the 377 cycles receiving r-ICSI only, 25 of the qualifying cases failed to have any fertilization, reducing TFF to 25/16 608 (0.15%). LIMITATIONS, REASONS FOR CAUTION: This was a single-center retrospective study on a specific subset of patients, which may limit its generalizability to other clinics. WIDER IMPLICATIONS OF THE FINDINGS: r-ICSI allows a second opportunity to fertilize oocytes despite poor initial outcomes. Patients who had a frozen blastocyst transfer achieved high live birth rates, indicating that a resynchronization of the embryo with the endometrium can optimize r-ICSI cases. r-ICSI allays fears of TFF when using C-IVF, providing evidence that the overuse of ICSI in patients without male factor may not be warranted. STUDY FUNDING/COMPETING INTEREST(S): The study was internally funded by Boston IVF. The authors declare that they have no conflict of interest in relation to the data published in the article. TRIAL REGISTRATION NUMBER: N/A.

Acceptance of genetic editing and of whole genome sequencing of human embryos by patients with infertility before and after the onset of the COVID-19 pandemic.

RESEARCH QUESTION: Has acceptance of heritable genome editing (HGE) and whole genome sequencing for preimplantation genetic testing (PGT-WGS) of human embryos changed after the onset of COVID-19 among infertility patients? DESIGN: A written survey conducted between April and June 2018 and July and December 2021 among patients at a university-affiliated infertility practice. The questionnaire ascertained the acceptance of HGE for specific therapeutic or genetic 'enhancement' indications and of PGT-WGS to prevent adult disease. RESULTS: In 2021 and 2018, 172 patients and 469 patients (response rates: 90% and 91%, respectively) completed the questionnaire. In 2021, significantly more participants reported a positive attitude towards HGE, for therapeutic and enhancement indications. In 2021 compared with 2018, respondents were more likely to use HGE to have healthy children with their own gametes (85% versus 77%), to reduce disease risk for adult-onset polygenic disorders (78% versus 67%), to increase life expectancy (55% versus 40%), intelligence (34% versus 26%) and creativity (33% versus 24%). Fifteen per cent of the 2021 group reported a more positive attitude towards HGE because of COVID-19 and less than 1% a more negative attitude. In contrast, support for PGT-WGS was similar in 2021 and 2018. CONCLUSIONS: A significantly increased acceptance of HGE was observed, but not of PGT-WGS, after the onset of COVID-19. Although the pandemic may have contributed to this change, the exact reasons remain unknown and warrant further investigation. Whether increased acceptability of HGE may indicate an increase in acceptability of emerging biomedical technologies in general needs further investigation.

ART outcomes in lean compared to obese phenotypes of polycystic ovarian syndrome.

RESEARCH QUESTION: To investigate differences in reproductive outcomes among IVF patients with lean compared to obese polycystic ovarian syndrome (PCOS) phenotypes. DESIGN: A retrospective cohort study of patients with PCOS who underwent IVF in a single, academically affiliated infertility center in the USA between December 2014 and July 2020. The diagnosis of PCOS was assigned based on Rotterdam criteria. Patients were designated as lean (< 25) or overweight/obese (≥ 25) PCOS phenotype based on BMI (kg/m2) at cycle start. Baseline clinical and endocrinologic laboratory panel, cycle characteristics, and reproductive outcomes were analyzed. The cumulative live birth rate included up to 6 consecutives cycles. A Cox proportional hazards model and Kaplan-Meier curve for estimating live birth rates were used to compare the two phenotypes. RESULTS: A total of 1395 patients who underwent 2348 IVF cycles were included. The mean (SD) BMI was 22.7 (2.4) in the lean and 33.8 (6.0) in the obese group (p < 0.001). A number of endocrinological parameters were similar between lean and obese phenotypes: total testosterone 30.8 ng/dl (19.5) vs 34.1 (21.9), p > 0.02 and pre-cycle hemoglobin A1C 5.33% (0.38) vs 5.51% (0.51) p > 0.001, respectively. The CLBR was higher in those with a lean PCOS phenotype: 61.7% (373/604) vs 54.0% (764/1414) respectively. Miscarriage rates were significantly higher for O-PCOS patients (19.7% (214/1084) vs 14.5% (82/563) p < 0.001) and the rate of aneuploids was similar (43.5%, 43.8%, p = 0.8). A Kaplan-Meier curve estimating the proportion of patients with a live birth was higher in the lean group (log-rank test p = 0.013). After adjusting for potential confounders, the lean phenotype was associated with an increased hazard ratio for live birth: HR = 1.38 p < 0.001. CONCLUSIONS: Lean PCOS phenotype is associated with a significantly higher CLBR compared to their obese counterparts. Miscarriage rates were significantly higher among obese patients, despite comparable pre-cycle HBA1C and similar aneuploidy rates in patients who underwent PGT-A.

Double strand DNA breaks in sperm: the bad guy in the crowd.

PURPOSE: The main objective of this opinion paper was to bring to light and enhance our understanding of the amount of double-strand DNA breaks in sperm and whether there is a threshold of no return when considering repair by the oocyte/embryo. METHODS: A brief review of literature related to the theories proposed for the appearance of double-strand breaks in human spermatozoa. Further commentary regarding their detection, how oocytes or embryos may deal with them, and what are the consequences if they are not repaired. Finally, a strategy for dealing with patients who have higher levels of double-strand DNA breaks in sperm is proposed by reviewing and presenting data using testicular extracted sperm. RESULTS: We propose a theory that a threshold may exist in the oocyte that allows either complete or partial DNA repair of impaired sperm. The closer that an embryo is exposed to the threshold, the more the effect on the ensuing embryo will fail to reach various milestones, including blastocyst stage, implantation, pregnancy loss, an adverse delivery outcome, or offspring health. We also present a summary of the role that testicular sperm extraction may play in improving outcomes for couples in which the male has a high double-strand DNA break level in his sperm. CONCLUSIONS: Double-strand DNA breaks in sperm provide a greater stress on repair mechanisms and challenge the threshold of repair in oocytes. It is therefore imperative that we improve our understanding and diagnostic ability of sperm DNA, and in particular, how double-strand DNA breaks originate and how an oocyte or embryo is able to deal with them.

Perinatal outcomes in 13,626 singleton pregnancies after autologous IVF across three continents over 7 years.

PURPOSE: Are trends in singleton autologous IVF perinatal outcomes consistent over time among five international infertility centers? METHODS: This was a retrospective cohort study from January 1, 2012, to December 31, 2018. This study was performed through a large infertility network at five international infertility centers in which patients who had a singleton live birth resulting from fresh and frozen autologous IVF cycles were included. The primary outcome was live birth weight (BW) with secondary outcomes of preterm birth (PTB), large for gestational age (LGA), small for gestational age (SGA), and gestational age at delivery. RESULTS: The entire cohort (n = 13,626) consisted of 6941 fresh and 6685 frozen autologous IVF cycles leading to singleton deliveries. Maternal age, parity, body mass index, neonatal sex, and GA at delivery were similar for fresh and frozen IVF cycles in the entire cohort and within each infertility center. Four centers had a trend of decreased BW and three centers had decreased rates of PTB before 32 and 28 weeks and LGA newborns annually, although significance was not reached. Three IVF centers had annual increased trends of PTB before 37 weeks and four centers had increased rates of SGA newborns, although significance was not reached. CONCLUSION: Similar trends in perinatal outcomes were present across five international infertility centers over 7 years. Additional studies are crucial to further assess and optimize perinatal outcomes at an international level.

Perinatal outcomes in 6640 singleton pregnancies after donor oocyte IVF across three continents over 7 years.

PURPOSE: Are trends in singleton donor oocyte IVF perinatal outcomes consistent over time among four international ethnically diverse infertility centers? METHODS: This retrospective cohort consisted of an infertility network of four international IVF centers across three continents. Singleton live births resulting from fresh and frozen donor oocyte embryo transfers from January 1, 2012 to December 31, 2018 were included. The main outcome measures were birth weight (BW), preterm birth (PTB), large for gestational age (LGA), small for gestational age (SGA) and gestational age (GA) at delivery. RESULTS: The entire cohort (n = 6640) consisted of 4753 fresh and 1887 frozen donor oocyte embryo transfers. Maternal age, parity, body mass index, neonatal sex and GA at delivery were similar for fresh and frozen donor oocyte embryo transfers in the entire cohort and within each infertility center. All four centers had a trend of decreased BW and rates of PTB before 32 weeks annually, although significance was not reached. Three of the four centers had annual increased trends of PTB before 37 weeks and LGA newborns, although significance was not reached. BWs for the entire cohort for fresh and frozen donor embryo transfers were 3166 g ± 601 g and 3137 g ± 626 g, respectively. CONCLUSION: Similar trends in perinatal outcomes were present across four international infertility centers over 7 years. The overall perinatal trends in donor oocyte IVF may be applicable to centers worldwide, but further studies in more geographic regions are needed.

RNA-seq as a tool for evaluating human embryo competence.

The majority of embryos created through in vitro fertilization (IVF) do not implant. It seems plausible that rates of implantation would improve if we had a better understanding of molecular factors affecting embryo competence. Currently, the process of selecting an embryo for uterine transfer uses an ad hoc combination of morphological criteria, the kinetics of development, and genetic testing for aneuploidy. However, no single criterion can ensure selection of a viable embryo. In contrast, RNA-sequencing (RNA-seq) of embryos could yield high-dimensional data, which may provide additional insight and illuminate the discrepancies among current selection criteria. Recent advances enabling the production of RNA-seq libraries from single cells have facilitated the application of this technique to the study of transcriptional events in early human development. However, these studies have not assessed the quality of their constituent embryos relative to commonly used embryological criteria. Here, we perform proof-of-principle advancement to embryo selection procedures by generating RNA-seq libraries from a trophectoderm biopsy as well as the remaining whole embryo. We combine state-of-the-art embryological methods with low-input RNA-seq to develop the first transcriptome-wide approach for assessing embryo competence. Specifically, we show the capacity of RNA-seq as a promising tool in preimplantation screening by showing that biopsies of an embryo can capture valuable information available in the whole embryo from which they are derived. Furthermore, we show that this technique can be used to generate a RNA-based digital karyotype and to identify candidate competence-associated genes. Together, these data establish the foundation for a future RNA-based diagnostic in IVF.

Fluorescence lifetime imaging microscopy (FLIM) detects differences in metabolic signatures between euploid and aneuploid human blastocysts.

STUDY QUESTION: Can non-invasive imaging with fluorescence lifetime imaging microscopy (FLIM) detect metabolic differences in euploid versus aneuploid human blastocysts? SUMMARY ANSWER: FLIM has identified significant metabolic differences between euploid and aneuploid blastocysts. WHAT IS KNOWN ALREADY: Prior studies have demonstrated that FLIM can detect metabolic differences in mouse oocytes and embryos and in discarded human blastocysts. STUDY DESIGN, SIZE, DURATION: This was a prospective observational study from August 2019 to February 2020. Embryo metabolic state was assessed using FLIM to measure the autofluorescence metabolic factors nicotinamide adenine dinucleotide dehydrogenase together with nicotinamide adenine phosphate dinucleotide dehydrogenase (NAD(P)H) and flavin adenine dinucleotide (FAD). Eight metabolic FLIM parameters were obtained from each blastocyst (four for NAD(P)H and four for FAD): short (T1) and long (T2) fluorescence lifetime, fluorescence intensity (I) and fraction of the molecules engaged with enzymes (F). The redox ratio (NAD(P)H-I)/(FAD-I) was also calculated for each image. PARTICIPANTS/MATERIALS, SETTING, METHODS: This study was performed at a single academically affiliated centre where there were 156 discarded frozen blastocysts (n = 17 euploids; 139 aneuploids) included. Ploidy status was determined by pre-implantation genetic testing for aneuploidy (PGT-A). Discarded human blastocysts were compared using single FLIM parameters. Additionally, inner cell mass (ICM) and trophectoderm (TE) were also evaluated. Multilevel models were used for analysis. A post-hoc correction used Benjamini-Hochberg's false discovery rate, at a q-value of 0.05. MAIN RESULTS AND THE ROLE OF CHANCE: Comparing euploid (n = 17) versus aneuploid (n = 139) embryos, a significant difference was seen in NAD(P)H-F (P < 0.04), FAD-I (P < 0.04) and redox ratio (P < 0.05). Euploid ICM (n = 15) versus aneuploid ICM (n = 119) also demonstrated significantly different signatures in NAD(P)H-F (P < 0.009), FAD-I (P < 0.03) and redox ratio (P < 0.03). Similarly, euploid TE (n = 15) versus aneuploid TE (n = 119) had significant differences in NAD(P)H-F (P < 0.0001) and FAD-I (P < 0.04). LIMITATIONS, REASONS FOR CAUTION: This study utilized discarded human blastocysts, and these embryos may differ metabolically from non-discarded human embryos. The blastocysts analysed were vitrified after PGT-A biopsy and it is unclear how the vitrification process may affect the metabolic profile of blastocysts. Our study was also limited by the small number of rare donated euploid embryos available for analysis. Euploid embryos are very rarely discarded due to their value to patients trying to conceive, which limits their use for research purposes. However, we controlled for the imbalance with the bootstrap resampling analysis. WIDER IMPLICATIONS OF THE FINDINGS: These findings provide preliminary evidence that FLIM may be a useful non-invasive clinical tool to assist in identifying the ploidy status of embryos. STUDY FUNDING/COMPETING INTEREST(S): The study was supported by the Blavatnik Biomedical Accelerator Grant at Harvard University. Becker and Hickl GmbH and Boston Electronics sponsored research with the loaning of equipment for FLIM. D.J.N. is an inventor on patent US20170039415A1. There are no other conflicts of interest to declare. TRIAL REGISTRATION NUMBER: N/A.

Metabolic state of human blastocysts measured by fluorescence lifetime imaging microscopy.

STUDY QUESTION: Can non-invasive metabolic imaging via fluorescence lifetime imaging microscopy (FLIM) detect variations in metabolic profiles between discarded human blastocysts? SUMMARY ANSWER: FLIM revealed extensive variations in the metabolic state of discarded human blastocysts associated with blastocyst development over 36 h, the day after fertilization and blastocyst developmental stage, as well as metabolic heterogeneity within individual blastocysts. WHAT IS KNOWN ALREADY: Mammalian embryos undergo large changes in metabolism over the course of preimplantation development. Embryo metabolism has long been linked to embryo viability, suggesting its potential utility in ART to aid in selecting high quality embryos. However, the metabolism of human embryos remains poorly characterized due to a lack of non-invasive methods to measure their metabolic state. STUDY DESIGN, SIZE, DURATION: We conducted a prospective observational study. We used 215 morphologically normal human embryos from 137 patients that were discarded and donated for research under an approved institutional review board protocol. These embryos were imaged using metabolic imaging via FLIM to measure the autofluorescence of two central coenzymes, nicotinamide adenine (phosphate) dinucleotide (NAD(P)H) and flavine adenine dinucleotide (FAD+), which are essential for cellular respiration and glycolysis. PARTICIPANTS/MATERIALS, SETTING, METHODS: Here, we used non-invasive FLIM to measure the metabolic state of human blastocysts. We first studied spatial patterns in the metabolic state within human blastocysts and the association of the metabolic state of the whole blastocysts with stage of expansion, day of development since fertilization and morphology. We explored the sensitivity of this technique in detecting metabolic variations between blastocysts from the same patient and between patients. Next, we explored whether FLIM can quantitatively measure metabolic changes through human blastocyst expansion and hatching via time-lapse imaging. For all test conditions, the level of significance was set at P < 0.05 after correction for multiple comparisons using Benjamini-Hochberg's false discovery rate. MAIN RESULTS AND THE ROLE OF CHANCE: We found that FLIM is sensitive enough to detect significant metabolic differences between blastocysts. We found that metabolic variations between blastocyst are partially explained by both the time since fertilization and their developmental expansion stage (P < 0.05), but not their morphological grade. Substantial metabolic variations between blastocysts from the same patients remain, even after controlling for these factors. We also observe significant metabolic heterogeneity within individual blastocysts, including between the inner cell mass and the trophectoderm, and between the portions of hatching blastocysts within and without the zona pellucida (P < 0.05). And finally, we observed that the metabolic state of human blastocysts continuously varies over time. LIMITATIONS, REASONS FOR CAUTION: Although we observed significant variations in metabolic parameters, our data are taken from human blastocysts that were discarded and donated for research and we do not know their clinical outcome. Moreover, the embryos used in this study are a mixture of aneuploid, euploid and embryos of unknown ploidy. WIDER IMPLICATIONS OF THE FINDINGS: This work reveals novel aspects of the metabolism of human blastocysts and suggests that FLIM is a promising approach to assess embryo viability through non-invasive, quantitative measurements of their metabolism. These results further demonstrate that FLIM can provide biologically relevant information that may be valuable for the assessment of embryo quality. STUDY FUNDING/COMPETING INTEREST(S): Supported by the Blavatnik Biomedical Accelerator Grant at Harvard University. Becker and Hickl GmbH and Boston Electronics sponsored research with the loaning of equipment for FLIM. D.J.N. is an inventor on patent US20170039415A1. TRIAL REGISTRATION NUMBER: N/A.