Faculty Bibliography

OBJECTIVE: It is well known that the embryo aneuploidy rate increases with women's age [1], but the effect of age on complex chromosomal abnormality (CCA) is less clear. Here, we addressed the relationship between maternal age and CCA with a retrospective cohort study. MATERIALS AND METHODS: We reviewed results of preimplantation genetic testing (PGT) by aCGH or NGS of embryo biopsies performed in an academic IVF unit between 2010 and 2019. We excluded PGT results from single gene disorder and egg donation cycles. CCA was defined as>=3 chromosome abnormalities (whole, partial and/or mosaic). Maternal age was categorized according to SART age groups: <35, 35-37, 38-40, 41-42, and >42 years. Statistical analyses were conducted using GraphPad Prism 8.
RESULT(S): 27,423 embryos were biopsied from 3,501 women aged 23 to 48 years. 4,740 embryos (16%) has CCA. Consistent with prior study [2], the most frequent chromosomes involved in CCA were 22, 16, 21 and 15, with incidences of 30.6%, 29.1%, 26.1% and 25.8% respectively. The number of chromosomal errors (from 3 to 42) involved in CCA did not correlate with maternal age (Spearman r = -0.0149, P = 0.3352). However, the rate of complex abnormal embryos tended to increase with advancing maternal age (9.7%, 11.2%, 10.9%, 24.8% and 43.6% in women aged < 35, 35-37, 38-40, 41-42, and > 42 years, respectively). Women over 40 years old had significantly higher rates of CCA compared to those under 40 years (Chisquare test, P < 0.0001). Surprisingly, the relationship between maternal age and CCA followed a U-shaped curve, decreasing from the 25 to 30 year old group (Pearson r = -0.831, P = 0.04) to the 30 to 35 year old group (Pearson r = 0.093, P = 0.861), then increased markedly in the 35 to 48 year old group (Pearson r = 0.921, P < 0.0001).
CONCLUSION(S):We found that CCA embryos share common features of aneuploidy, such as association with maternal age and preferential involvement of shorter chromosomes i.e. 22, 16, 21 and 15. Unexpectedly, our data showed that the relationship between CCA and maternal age assumes a U shape with increased rates at very young and very old ages. Both meiotic and mitotic errors contribute to chromosomal abnormality, and the contribution of each to CCA merits further investigation. IMPACT STATEMENT: The complex relationship between maternal age and embryo aneuploidy, which approximates a U-shape, may inform optimal timing of elective oocyte freezing and oocyte donation

OBJECTIVE: Oocyte cryo is widely used for fertility preservation, but the value of M1 cryo remains unclear. We evaluated the utility and efficiency of M1 compared to M2 cryo. MATERIALS AND METHODS: Patients (pts) who thawed autologous oocytes at our academic center from 2004-2020 were reviewed. Pts were excluded if cryo was performed for a medical indication, as research, due to no sperm or a natural disaster, in combination with embryos or for use with a gestational carrier. At our center, all M1s retrieved from 2004-2015 were cryopreserved; after 2015, M1s were only cryopreserved if <15 M2s were retrieved during the same cryo cycle. Outcomes included survival rate, useable embryo rate and embryo transfer (ET) results.Auseable embryo was defined as an embryo that was transferred, biopsied or cryopreserved for future use. Statistics included Fisher's exact test.
RESULT(S): 543 pts (median age at 1st cryo 38y, interquartile range 37-40y) underwent 800 cryo, 605 thaw and 416 ET cycles. Cryo was performed with vitrification for 72%, slow freezing for 4% and both technologies for 24% of pts. In total, 8511 oocytes (1019M1s + 7492 M2s)were thawed.All pts thawed >=1 M2, and 60% (n=327) thawed >=1 M1. See table for thaw outcomes of M1s vs. M2s. For 30 pts, >=1 M1 led to a useable embryo (n=32 useable embryos). Vitrification was used for 69% of these M1s (n=22) and slow freezing was used for 31% (n=10). Of the 32 useable embryos from M1s, 69% (n=22) underwent PGTand 4were euploid (17 aneuploid, 1 mosaic). Therewere 3 single ETs of euploid embryos from M1s, which led to 1 spontaneous abortion (SAB) and 2 biochemical pregnancies. Therewere 3 single ETs of untested embryos from M1s, which led to 1 negative result, 1 SAB and 1 singleton ongoing pregnancy. The ongoing pregnancy is from an ETof a day 5 morula and is now in the third trimester. There were 6 ETs in which untested embryos from M1s were transferred alongwith untested embryos fromM2s, resulting in 3 negative results, 1 SAB, 1 singleton live birth and 1 unknown outcome (ongoing singleton pregnancy at last contact).
CONCLUSION(S): Cryopreserved M1s can result in useable embryos and pregnancies, but are less likely to survive or form useable embryos than cryopreserved M2s. To our knowledge, this is the first report of an ongoing third trimester pregnancy from a cryopreserved M1. This information may be helpful for pt counselling and designing oocyte cryo protocols for embryology labs. IMPACT STATEMENT: Cryopreserved M1s may be a viable option for pts with a low M2 yield. (Table Presented)

OBJECTIVE: OC is widely used for fertility preservation. Many models predict the live birth (LB) rate of OC, but real-world data is lacking. We reviewed our LBs from OC to develop an OC counseling tool based on real outcomes. MATERIALS AND METHODS: We reviewed patients (pts) who thawed autologous oocytes (AOs) at our academic fertility center from 2004-2020. We included pts who: 1) had a LB or ongoing pregnancy (OP) >12 weeks at last contact, or 2) consumed all AOs and resultant embryos. Pts were excluded if they transferred AOs or resultant embryos to another center or if OC was performed for a medical reason, as research, due to no sperm or a natural disaster, combined with embryos or for use with a gestational carrier. We calculated OP + LB rate (LBR) based on number of AOs and metaphase II oocytes (M2s) thawed. Data were stratified by age (<38y vs. >=38y). For pts who underwent OC at <38y and >=38y, a weighted age was calculated (for each OC cycle, #AOs thawed was multiplied by age at OC; the sum of these numbers was then divided by total #AOs thawed). Statistics included Fisher's exact test (p<0.05 significant).
RESULT(S): We included 462 pts (median age at 1st OC 38.5y). Weighted ages were used for 21 pts (5%). Our pts underwent 650 OCs (90% our center, 9% elsewhere, 1% both), 512 thaws and 385 embryo transfers. OC involved vitrification for 72%, slow freezing for 4% and both for 24% of pts. A total of 7050 AOs and 6178 M2s were thawed. 38% of pts (n=176) have >=1 LB or OP from AO thaw. See table for outcomes. Pts who thawed 0-10 AOs had a lower LBR than pts who thawed 11-20, 21-30, or >30 AOs (p<=0.03). Pts who thawed 0-10 M2s had a lower LBR than pts who thawed 11-20 or 21- 30 M2s (p<=0.02). LBR was not significantly different between pts who thawed 11-20, 21-30, or >30 AOs or M2s.
CONCLUSION(S): Pts who thawed 0-10 AOs had a lower LBR (27%) than pts who thawed >10 AOs (LBR >= 43%), and pts who thawed 0-10 M2s had a lower LBR (30%) than pts who thawed > 10 M2s (LBR >= 42%), but LBR was not different with >10 thawed AOs. IMPACT STATEMENT: Our real-world OC outcomes are not consistent with LBRs in published models. These results provide more realistic expectations about OC outcomes and may help pts decide how many AOs to freeze

OBJECTIVE: Mosaic embryo transfer (MET) following preimplantation genetic testing for aneuploidy (PGT-A) has become more commonplace, particularly among patients who do not have any euploid embryos available for transfer. Our aim was to report on uptake and results of prenatal diagnosis (PND) following MET. MATERIALS AND METHODS: All MET cases occurring at our clinic between September 2015 and February 2021 in which an ongoing pregnancy was documented were reviewed. Patients received genetic counseling prior to MET, including discussion of prenatal testing options, and a summary letter was provided upon discharge. Medical records were reviewed to determine whether PND was performed, and the types of analyses performed on amniotic fluid (AF) or chorionic villi (CV).
RESULT(S): Sixty-five patients had an ongoing pregnancy following MET. Eight patients were excluded from the analysis due to gestational age too early for PND, and we were able to obtain PND results for 33 of the 57 patients (57.9%). Of the remaining patients, 9/57 (15.8%) declined PND, and we were unable to obtain information about whether PND was performed for 15/57 (26.3%). Since 2/33 patients were carrying twins both originating from MET, there were a total of 35 conceptuses with PND results; 34 on AF and 1 on CV. In one case, spontaneous abortion (SAB) occurred following attempted amniocentesis and was attributed to an infection caused by the procedure. In 35/35 cases (100%), karyotype results were normal (46,XY or 46,XX). In 28/35 cases (80.0%), chromosomal microarray was also performed, and there were no cases in which segmental mosaicism identified in the embryo was detected. In 6/28 cases (21.4%), a variant of uncertain significance (VUS) was identified on a different chromosome; 5/6 of which were inherited from a parent and were below the resolution of PGT-A (mean size 206.6 kb). Two out of 35 cases (5.7%) involved additional uniparental disomy (UPD) analysis; one result was normal while the other was inconclusive due to lack of informative parental markers.
CONCLUSION(S): There were no cases identified in which PND results confirmed mosaicism detected by PGT-A; therefore, this risk appears to be low. Genetic counseling about MET should address benefits, limitations, and risks of PND, including potential of an unrelated VUS and procedurerelated risk of SAB. Currently, it remains unclear as to whether the benefits of PND outweighs these risks, and whether additional analyses such as UPD testing are warranted. Future studies are necessary to determine whether specific types of mosaic results are associated with different risks, as well as the psychological impact of PND after MET on patients. IMPACT STATEMENT: Our study provides evidence that the risks associated with METare likely overestimated, as we did not identify any cases of abnormal PND consistent with the mosaic PGT-A result. These data are necessary for accurate patient counseling and informed consent, as well as evidence-based clinical policy development

OBJECTIVE: Many preimplantation genetic testing (PGT) labs require intracytoplasmic sperm injection (ICSI) for PGT for aneuploidy (PGT-A) due to concern for paternal cell contamination. We sought to determine if sperm lysis occurs during PGT-A and assess the rate of paternal cell contamination in trophectoderm (TE) biopsies in embryos from insemination. MATERIALS AND METHODS: Sixty-two tripronuclear (3PN) embryos donated to research were collected from IVF with either insemination or ICSI from January - April, 2021. Embryos were cultured and assessed for development to blastocyst stage on days 5, 6 and 7 of culture. Embryos that developed into blastocysts underwent two separate TE biopsies. Biopsy procedure consisted of zona ablation on day 4 followed by TE biopsy using 2-3 pulses of laser beam at the cell junction. Biopsy samples were washed with drops of buffer 2-3 times and placed in a PCR tube. Arrested embryos were collected and assessed for approximate cell number. One group of arrested embryos was collected without washing (unwashed) and a second group was collected after removal of the zona (washed). TE biopsies, arrested embryos, and maternal and paternal samples were sent to a PGT lab to determine the genetic ploidy composition of the embryo biopsies and arrested embryos including the parent of origin. Testing included PGT-A using the PGTseq platform and SNP allele sharing that can detect parental origin of abnormalities and contamination.
RESULT(S): Of the 62 3PN embryos cultured, 17 developed into blastocysts with 4 from ICSI and 13 from insemination. There were 45 arrested embryos with 6 from ICSI (2 washed, 4 unwashed) and 39 from insemination (14 washed, 25 unwashed). PGT analysis showed varying degrees of paternal cell contamination in unwashed arrested embryos from insemination, and no paternal cell contamination in washed arrested embryos (ICSI or insemination) or unwashed ICSI embryos. Two washed arrested embryos from insemination showed no amplification. There was no paternal cell contamination in TE biopsies from either ICSI or insemination.
CONCLUSION(S): Analysis of unwashed arrested embryos from insemination demonstrates that excess sperm can lyse and cause paternal cell contamination during PGT-A. However, TE biopsies of embryos from insemination showed no evidence of paternal cell contamination, indicating that when properly washed and processed, paternal cell contamination is unlikely in inseminated embryos undergoing PGT-A. While this study was not powered to draw definitive conclusions or assess levels of contamination that interfere with PGT-A, preliminary results indicate that ICSI is not necessary for PGT-A. It should be noted that these findings are specific to the PGTseq platform, and may not translate to other methods. IMPACT STATEMENT: This study demonstrates that sperm have the ability to lyse and are a potential source of paternal cell contamination in PGT-A. However, this study also showed a 0% rate of paternal cell contamination in inseminated embryos when embryo biopsies were washed and processed as described, suggesting that ICSI is not necessary for patients desiring PGT-A

OBJECTIVE: To compare three different implantation prediction models using artificial intelligence algorithms (AI) that analyze (I) morphology only, (II) morphokinetic events only using an automatic AI-based annotation model, and (III) a combination of both, in a retrospective multi-center study. MATERIALS AND METHODS: The automatic morphokinetic evaluation tool was trained on 36561 annotated embryos obtained between 2014 - 2019 (34132 in training set and 2429 in test set). Morphokinetic annotation and morphology evaluation of 6938 embryos with known implantation data (KID) were used to train and test KID+TM, an AI algorithm. The training set consisted of 6363 embryos (1078 KID-positive and 5285 KID-negative). The blind test set consisted of 575 embryos (171 KID-positive and 404 KID-negative). KID+TM scored the embryos for implantation potential based on an automatic evaluation of morphokinetic and morphology data. We compared our combined morphokinetic and morphology model KID+TM to (I) a model that only considers morphokinetic events and (II) a model that only considers morphology from the last frame of embryo development.
RESULT(S): We aimed to compare the implantation prediction potential of algorithms that analyze morphokinetic features only, morphology features only, and a combination of both. To accomplish this, we trained a convolutional neural network (CNN) to perform automatic annotations of embryo development events (r² =0.95). Analysis of these estimated annotations revealed a robust implantation prediction tool with an area under curve (AUC) continuously increasing from 30 to 116 hours post insemination, reaching a maximal AUC of 0.65 at 116 hours. However, single image analysis of the last frame of the embryo video after the morula stage demonstrated better prediction with AUC of 0.68 at 116 hours. Thus, the combined morphokinetic and morphology algorithm was valuable for implantation prediction until the start of blastulation (~90 hours). After the start of blastulation, the combined algorithm did not demonstrate a superior AUC relative to the morphology only algorithm with an AUC of 0.68 at 116 hours.
CONCLUSION(S): The combined morphokinetic and morphology algorithm was more effective for implantation prediction at the cleavage stage than the morphology only algorithm. Thus, the combined algorithm has the potential to improve the embryo selection process for day 3 transfers. In the later stages of embryo development, the morphology only algorithm was as effective for implantation prediction as the combined algorithm. IMPACT STATEMENT: AI models have the potential to eliminate the high degree of inter- and intra-observer variability associated with embryo assessment by automating morphokinetic and morphology evaluation to accurately predict embryo outcomes, thereby improving IVF outcomes. In addition, AI models leveraging morphokinetic and morphology data may be able to accurately evaluate embryos in earlier stages of development to improve selection for day 3 transfers

OBJECTIVE: To compare telomere length (TL) and telomerase gene expression in human euploid and aneuploid blastocysts generated from IVF treatment. MATERIALS AND METHODS: TL and telomerase gene expression were measured in cryopreserved aneuploid (N=115) and euploid (N=4) human blastocysts donated by 26 patients who consented research under approval of IRB study #16-00154. Blastocysts were classified according to number of aneuploid chromosomes (A1-one segmental error, A2-one whole chromosome error, A3-two chromosomal errors and A4- >= 3 chromosomal errors). Genomic DNA and messenger RNA were separated simultaneously from individual blastocysts after thawing in vitrification-warming media. Telomerase reverse transcriptase (TERT) and telomerase RNA component (TERC) mRNA levels were determined by RT-qPCR with GAPDH as internal control, and TL was measured by qPCR with 5s rDNA as internal control. Relative gene expression and TL were calculated by DELTADELTA^Ct method, and GraphPad Prism 8 software was used for statistical analysis.
RESULT(S): TL and telomerase gene expression were not normally distributed, so nonparametric tests were used to compare the medians among groups (Table 1). Median TL, TERTand TERC levels didn't differ by number of chromosome errors nor between aneuploid and euploid groups. Intriguingly, TL, TERT and TERC levels in aneuploid blastocysts tended to be greater compared to euploid blastocysts. TL in blastocysts correlated with telomerase TERT expression (R² =0.054, P = 0.011), but not TERC expression (R² =0.0002, P = 0.865).
CONCLUSION(S): To our knowledge, this is the largest study to measure telomere length and telomerase gene expression in human blastocysts. Our data indicated that telomeres are lengthened and telomerase is activated in aneuploid embryos at blastocyst stage. Moreover, telomere length and telomerase gene TERT in human blastocysts correlate regardless of ploidy status. Like cancer cells, TERT is highly expressed in aneuploid blastocysts. IMPACT STATEMENT: Robust TERT expression and telomere maintenance in aneuploid human blastocysts may explain why extended in vitro culture alone is insufficient to cull out aneuploidy embryos during IVF (Table Presented)

OBJECTIVE: To determine the prognostic utility of day of biopsy on mosaic embryo (ME) transfer outcomes. MATERIALS AND METHODS: Sub-analysis was performed of data collected in the 2021 study by Viotti et al 1. Descriptive statistics (mean +/- standard deviation for continuous variables; frequencies and percentages for categorical variables) were calculated separately by biopsy day (5, 6, or 7). The three groups were compared using the chi-square test or Fisher's exact test, as deemed appropriate, for categorical variables, and analysis of variance (ANOVA) for continuous data. A result was considered statistically significant at p<0.05. All analyses were performed using SAS version 9.4 (SAS Institute Inc., Cary, NC).
RESULT(S): Of the 1000 ME transfers documented, 825 specified day of biopsy (day 5, 6, or 7). There was a significant difference in mosaic type by biopsy day (p<0.0001); day 7 MEs resulted in significantly more complex and single monosomy/trisomy types. Day 6 MEs resulted in significantly more double monosomy/trisomy type. Day 5 MEs resulted in significantly more segmental types overall, including single, double, and complex segmental. There were also significant differences in outcomes; day 7 MEs were significantly less likely to result in pregnancy (p=0.0015), while day 5 MEs were significantly more likely to result in implantation (p= 0.0005) and ongoing pregnancy/live birth (p <0.0001). There was no significant difference in biochemical pregnancy (p= 0.717) or spontaneous abortion (p=0.757) based on biopsy day. There was no significant difference in maternal age (p= 0.455) or percent mosaicism (p=0.319) based on biopsy day. Day 5 MEs had significantly better morphology (p< 0.0001). The difference in ongoing pregnancy rate among the three biopsy days remained statistically significant after adjusting for mosaic type (p<0.0005). However, there was no significant difference in ongoing pregnancy rate between mosaic types after adjusting for biopsy day (p=0.1369).
CONCLUSION(S): MEs biopsied on day 5 are more likely to have segmental type mosaicism, better morphology, and better transfer outcomes. The mechanism for these differences are unclear; however, a hypothesis is that embryos with mosaicism associated with poorer outcomes may be slower to develop into blastocysts. These data can be incorporated into ME prioritization decisions. Further studies are needed to determine whether larger sample sizes would show similar findings, and how biopsy day can be combined with embryo morphology and mosaic type to continue improving ME selection and better inform patient counseling. IMPACT STATEMENT: Day of embryo biopsy is an important predictor of ME transfer success

OBJECTIVE: AO cryopreservation (cryo) is widely used, but published thaw data is scarce. We reviewed our elective AO thaws. MATERIALS AND METHODS: Pts who thawed AOs at our FC in 2004- 2020 were reviewed. Pts were excluded if AO cryo was performed for a medical reason, as research, due to no sperm or a natural disaster, with embryo cryo or for use with a gestational carrier. Outcomes included implantation (IR), spontaneous abortion (SABR) and ongoing pregnancy + live birth (LBR) rates / embryo transfer (ET). We calculated a final LBR (FLBR) defined as LBR / pt; FLBR only included pts who a) had live birth (LB) or ongoing pregnancy (OP), or b) consumed all AOs and resultant embryos. Statistics included Mann-Whitney U and Fisher's exact test.
RESULT(S): 543 pts (median age at 1st cryo 38y) underwent 800 cryos (89% our FC, 9% elsewhere, 2% both), 605 thaws and 416 ETs. Cryo used vitrification for 72%, slow freezing for 4% and both for 24% of pts. Median time from 1st cryo to 1st thaw was 4y. In total, we thawed 8511 AOs (7492 M2s). AO survival was 79%, M2 survival was 80% and 2PN fertilization was 66%. When pts returned for thaw, 25% pursued fresh ET, 73% pursued preimplantation genetic testing (PGT), and 2% pursued a combination of both. In pts who pursued fresh ET, 92% had >=1 embryo for ET. In pts who pursued PGT, 57% had >=1 euploid. 13% of pts had no useable embryos (embryos for fresh ET, PGT, cryo). 59% of pts had >=1 ET. 37% of ETs were fresh, with 2% using rush-PGT. 63% of ETs were frozen, with 97% using PGT. In non-biopsied ETs, IR was 29%, SABR was 19% and LBR was 31%. In euploid ETs, IR was 64%, SABR was 10% and LBR was 55%. In our cohort, FLBR was 38%. In total, 178 babies (11 twin, 1 triplet) and 24 OPs resulted. 176 pts have >=1 LB or OP, and 23 pts have >=2 LBs or OPs from AO thaw. 33% of pts have remaining AOs or euploid or untested embryos; 45% of these pts do not have a LB or OP from AO thaw. See table for outcomes by age.
CONCLUSION(S): AO thaw leads to a FLBR of 38%, comparable to our FC's 34% LBR per intended retrieval in pts of similar age1 . IMPACT STATEMENT: Our real thaw data may be more useful than models in pt counseling

Study question: To explore the effect of chromosomal mosaicism detected in preimplantation genetic testing (PGT-A) on prenatal and postnatal outcome of mosaic embryo pregnancies Summary answer: No significant difference between euploid and mosaic embryos was observed in terms of weeks of gestation, average weight, and developmental defect of the babies born What is known already: Mosaic embryos have the potential to implant and develop into healthy babies.Transfer of these embryos is now offered as an option for women who undergo IVF resulting in no euploid embryos. While, prenatal diagnosis has shown the depletion of chromosomal mosaicism in mosaic embryos, several concerns remain. For instance, the direct effects of different kind of mosaicism on prenatal/postnatal outcome and the possibility that intra-biopsy mosaicism in the TE is a poor predictor of the ploidy status of the ICM. Thus, there is certainly a need for comprehensive analyses of obstetrical and neonatal outcome data of transferred mosaic embryos. Study design, size, duration: Compiled analysis from multicenter data on transfers of mosaic embryos (n=1,000) and their outcome, with comparison to a euploid control group (n=5,561). To explore the effect of embryonic mosaicism on newborns, we matched mosaic embryos resulting in a birth with a euploid embryo by a series of parameters (maternal age, embryo morphology, and indication for PGT-A). Prenatal tests and birth characteristics of >200 neonates from mosaic embryo transfers were compared to >200 euploid embryos. Participants/materials, setting, methods: PGT-A was performed on blastocyst- stage embryos with 24-Chromosome whole genome amplification (WGA)-based Next Generation Sequencing (NGS). In accordance with established guidelines, embryos were categorized as mosaic when PGT-A results indicated 20-80% aneuploid content. Prenatal testing where performed in 30% of pregnancies with amniocentesis, 4% did an extra analysis for potential UPD for the suspected mosaic chromosome, and an additional 16% performed chorionic villus sampling (CVS) and 9.5% performed noninvasive prenatal testing (NIPT). Main results and the role of chance: Of the 465 mosaic embryos that implanted, about 20% miscarried, and out of those, 75% were early spontaneous abortions. Of the pregnancies, 3 out of 368 were stillborn (2 out of them were twins that were extremely premature at 23 weeks, and the other died during pregnancy from a heart defect). The remaining 99% of those have been born or are late ongoing pregnancies at the time of analysis. Prenatal tests were performed in >200 pregnancies and the vast majority tested normal. All 5 abnormal cases were amniocentesis tests showing microdeletions or insertions of sizes smaller than the resolution used during PGT-A, so they were unrelated to the mosaicism detected with PGT-A. In fact, in none of the cases did the prenatal test reflect the mosaicism detected at the embryonic stage. Matching each of the 162 mosaic embryos resulting in a birth with a euploid embryo, we found that the length of gestation was similar on average, and so was the average weight of the babies at birth. We also gathered information on the routine physical examination performed on babies at birth, and of those 162 babies from mosaic embryo transfers, none had obvious developmental defects or gross abnormalities. Limitations, reasons for caution: Even though newborns resulting from mosaic embryo transfers in this study invariably appeared healthy by routine examination, concerns for long-term health cannot yet be entirely dispelled. The question must therefore be carefully considered by each clinic and patient situation. Wider implications of the findings: Prenatal testing of >200 pregnancies from mosaic embryo transfers showed no incidence of mosaicism that matched the PGT-A findings, indicating the involvement of self-corrective mechanisms. Pregnancy and obstetric data indicates that mosaic embryos prevailing through gestation and birth have similar chromosomal and physiological health compared to euploid embryos