Summary Chromosome imbalance (aneuploidy) is the major cause of pregnancy loss and congenital disorders in humans. Analyses of small biopsies from human embryos suggest that aneuploidy commonly originates during early divisions, resulting in mosaicism. However, the developmental potential of mosaic embryos remains unclear. We followed the distribution of aneuploid chromosomes across 73 unselected preimplantation embryos and 365 biopsies, sampled from four multifocal trophectoderm (TE) samples and the inner cell mass (ICM). When mosaicism impacted fewer than 50% of cells in one TE biopsy (low-medium mosaicism), only 1% of aneuploidies affected other portions of the embryo. A double-blinded prospective non-selection trial (NCT03673592) showed equivalent live-birth rates and miscarriage rates across 484 euploid, 282 low-grade mosaic, and 131 medium-grade mosaic embryos. No instances of mosaicism or uniparental disomy were detected in the ensuing pregnancies or newborns, and obstetrical and neonatal outcomes were similar between the study groups. Thus, low-medium mosaicism in the trophectoderm mostly arises after TE and ICM differentiation, and such embryos have equivalent developmental potential as fully euploid ones.

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Objective: To study the actual controlled ovarian stimulation (COS) management in women with suboptimal response, comparing clinical outcomes to the gonadotropins consume, considering potential role of luteinizing hormone (LH) addition to follicle-stimulating hormone (FSH). Design: Monocentric, observational, retrospective, real-world, clinical trial on fresh intra-cytoplasmic sperm injection (ICSI) cycles retrieving from 1 to 9 oocytes, performed at Humanitas Fertility Center from January 1st, 2012 to December 31st, 2015. Methods: COS protocols provided gonadotropin releasing-hormone (GnRH) agonist long, flare-up, short and antagonist. Both recombinant and urinary FSH were used for COS and LH was added according to the clinical practice. ICSI outcomes considered were: gonadotropins dosages; total, mature, injected and frozen oocytes; cumulative, transferred and frozen embryos; implantation rate; pregnancy, delivery and miscarriage rates. Outcomes were compared according to the gonadotropin regimen used during COS. Results: Our cohort showed 20.8% of low responders, defined as 1–3 oocytes retrieved and 79.2% of “suboptimal” responders, defined as 4–9 oocytes retrieved. According to recent POSEIDON stratification, cycles were divided in group 1 (6.9%), 2 (19.8%), 3 (11.7%), and 4 (61.5%). The cohort was divided in 3 groups, according to the gonadotropin's regimen. Women treated with FSH plus LH showed worst prognostic factors, in terms of age, basal FSH, AMH, and AFC. This difference was evident in suboptimal responders, whereas only AMH and AFC were different among treatment groups in low responders. Although a different result, in terms of oocytes and embryos detected, major ICSI outcomes (i.e., pregnancy and delivery rates) were similar among groups of COS treatment. Outcomes were significantly different among Poseidon groups. Implantation, pregnancy and delivery rates were significantly higher in Poseidon group 1 and progressively declined in other POSEIDON groups, reaching the worst percentage in group 4. Conclusions: In clinical practice, women with worst prognosis factors are generally treated with a combination of LH and FSH. Despite low prognosis women showed a reduced number of oocytes retrieved, the final ICSI outcome, in terms of pregnancy, is similarly among treatment group. This result suggests that the LH addition to FSH during COS could improve the quality of oocytes retrieved, balancing those differences that are evident at baseline. Clinical Trial Registration: www.ClinicalTrials.gov , identifier: NCT03290911

Background Next generation sequencing (NGS) has increased detection sensitivity of intermediate chromosome copy number variations (CNV) consistent with chromosomal mosaicism. Recently, this methodology has found application in preimplantation genetic testing (PGT) of trophectoderm (TE) biopsies collected from IVF-generated human embryos. As a consequence, the detection rate of intermediate CNV states in IVF embryos has drastically increased, posing questions about the accuracy in identifying genuine mosaicism in highly heterogeneous biological specimens. The association between analytical values consistent with mosaicism and the reproductive potential of the embryo, as well as newborn's chromosomal normalcy, have not yet been thoroughly determined. Methods We conducted a multicentre, double-blinded, non-selection trial including 1,190 patients undergoing in a total of 1,337 IVF with preimplantation genetic testing for aneuploidies (PGT-A) treatment cycles. NGS was performed on clinical TE biopsies collected from blastocyst-stage embryos. All embryos were reported as euploid if all autosomes had a chromosomal copy number value below the threshold of 50% abnormal cells per sample. After embryo transfer, three comparative classes were analysed: uniformly euploid profiles (<20% aneuploid cells), putative low-degree mosaicism (20%-30% aneuploid cells) or putative moderate-degree mosaicism (30%-50% aneuploid cells). Primary outcome measure was live birth rate (LBR) per transfer and newborn's karyotype. Results LBR after transfer of uniformly euploid embryos, low-degree, and moderate-degree mosaic embryos were 43.4% (95% C.I. 38.9 - 47.9), 42.9% (95% C.I. 37.1 - 48.9) and 42% (95% C.I. 33.4 - 50.9), respectively. No difference was detected for this primary outcome between euploid and mosaic low/moderate categories (OR= 0.96; 95% CI 0.743 to 1.263; P=0.816). The non-inferiority endpoint was met as the confidence interval for the difference fell below the planned 7.5% margin (95% C.I. -5.7 - 7.3). Likewise, no statistically significant difference was observed comparing moderate versus low degree mosaic embryos (P=0.92). Neonatal karyotypes were also similar and no instances of mosaicism or uniparental disomies (UPDs) were detected in babies born following putative low or moderate-degree mosaic embryo transfer. Should the embryos with low or moderate-degree mosaic TE biopsies had been classified as chromosomally abnormal and thus discarded for clinical use, LBR per cycle would have decreased by 36% without any clinical benefit. Conclusions This prospective non-selection trial provides substantial evidence that reporting and/or not transferring embryos with low/moderate-degree mosaicism for whole chromosomes have no clinical utility. Moreover, dismissing these embryos from clinical use has the counterproductive effect of reducing overall embryo availability, thus reducing the chance of successful outcome derived from an IVF treatment without any clinical benefit. (Funded by Igenomix; ClinicalTrials.gov number, NCT03673592)

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