O-174 The association of chromosomal abnormalities with embryo ultrastructure, spindle anomalies and metabolic profiling

Study question

Can metabolic profiling predict embryos at risk of chromosomal abnormalities and how are these reflected in the ultrustructure and cytoskeleton?

Summary answer

Different metabolic profiles are observed between normal and aneuploid/chaotic embryos which are linked to altered mitochondrial and other organelles’ structure/function and spindle and nuclear abnormalities.

What is known already

One of the greatest challenges in IVF is the selection of the best ‘fit’ embryo for implantation in a non-invasive way. Down’s syndrome embryos and Monosomy 21 embryos have previously been shown to have differential expression of metabolites compared to normal embryos, but limited studies, have investigated in detail the metabolic profiling of embryos with other abnormalities in comparison to chromosomally normal embryos or their reflection in the ultrustructure and the cytoskeleton.

Study design, size, duration

Culture media collected on day 3 from 200 embryos which underwent PGT-A, were analysed by hydrophilic interaction liquid chromatography tandem mass spectrometry (HILIC-MS/MS). The chromosomally normal embryos were transferred to the uterus (1–2 embryos/ET) or still remain vitrified for clinical use and 120 of the embryos that were diagnosed with chromosomal abnormalities were either processed for spindle/chromosome configurations analysis (n = 60) by confocal laser scanning microscopy(CLSM) or for ultrastructural analysis (n = 60) by Transmission Electron Microscopy(TEM).

Participants/materials, setting, methods

Metabolic profiling was conducted in a Forensic Toxicology Laboratory by HILIC-MS/MS (100 metabolites). Spindle Chromosome Configuration analysis was conducted in an academic hospital after methanol fixation and immunostaining with α-tubulin, γ-tubulin, acetylated-tubulin antibodies and DAPI or/ PI to visualise DNA. Ultrastructure analysis by TEM was carried out in a Histology/Embryology Laboratory following embryo fixation in 3% glutaraldehyde, 1% osmium tetroxide, washes in  PBS and staining with 1% aqueous uranyl acetate.

Main results and the role of chance

This  study provides screening  for >100 primary metabolites using HILIC-MS/MS in a single run of 40 minutes. Characteristic patient specific metabolic profiles were observed which differed between normal embryos that had resulted in a viable pregnancy and aneuploid and chaotic embryos. Logistic regression analysis revealed a number of metabolites that had a high predictive value including Isoleucine,  lysine and glucose and models were created in combination with embryo score which in the future could serve as non-invasive markers for the detection of chromosomal abnormalities before embryo transfer. TEM analysis revealed differences in the quality of cells and organelle activity which were reflected in the embryo metabolic profiles. Chaotic poor quality embryos showed a lower number of mitochondria, often with no cisternae, increased number of vacuoles, and frequently problems in junctions between cells. Aneuploid but well developed hatching blastocysts had mainly cells with good mitochondrial morphology/ activity, nice Golgi apparatus and well developed rough and smooth endoplasmic reticulum but depending on the aneuploidy involved, inner cell mass cells with limited organelles and occasionally lipofuscin droplets in the trophectoderm were evident. Nuclear and chromosomal abnormalities were interrelated through abnormalities in cytokinesis and spindle formation and reflected in the embryo metabolic profiles.

Limitations, reasons for caution

Although metabolic profiles were compared between normal and chromosomally abnormal embryos identified by PGT-A, all the  normal embryos were transferred to the uterus or remain vitrified for clinical purposes and therefore the ultrastructure analysis and the spindle chromosome configuration analysis are based only on chromosomally abnormal embryos.

Wider implications of the findings

This study identified distinct differences in the metabolic profiles of normal and chromosomally abnormal embryos and provides unique metabolites which in the future could serve as non-invasive biomarkers for the detection of chromosomal abnormalities before embryo transfer.

Trial registration number

not applicable

P–261 The human embryo following biopsy on day5 vs day3: Implantation, cytoskeleton, ultrastructure and effects of endometrial damage/inflammation on receptivity as revealed by scanning electron microscopy

Study question

Are there any differences in implantation, cytoskeleton and ultrastructure of embryos biopsied on day5 vs day3 and how endometrial damage/inflammation may affect receptivity and implantation?

Summary answer

No differences are observed in implantation rates but vitrification following day5 biopsy led to more cytoskeletal/ultrastructural anomalies. Infections and epithelial damage severely affected endometrial receptivity.

What is known already

Successful implantation is dependent on the correct synchronization of the window of implantantation with the transfer of chromosomally/genetically normal embryos, in a well prepared receptive endometrium. This is the first study to examine the effects of day5 vs day3 embryo biopsy by comparing implantation/pregnancy rates and by analysing cytoskeleton using Confocal Laser Scanning Microscopy (CLSM), and ultrastructure by Transmission Electron Microscopy (TEM). In addition, Scanning Electron Microscopy (SEM) was used on endometrial biopsies to assess possible uterine pathologies/inflammation that may be responsible for the failed implantation after PGT-A/M and if subsequent treatment can increase implantation/pregnancy rates in succeeding PGT-A/M cycles.

Study design, size, duration

470 embryos were biopsied on day5 for PGT-A (n = 152–37 cycles) or on day3 for PGT-A (n = 162–29 cycles) and PGT-M (n = 156–22 cycles). Following transfer of normal embryos, spare embryos, rejected for transfer following day5 or day3 biopsy were processed for Cytoskeletal analysis (n = 30 fresh day3 biopsied, n = 30 day5 biopsied/vitrified) or TEM (n = 20 fresh day3 biopsied, n = 20 day5 biopsied/vitrified). Also, patients with a –ve hCG test, underwent endometrial biopsy to detect infection/inflammation and assess receptivity.

Participants/materials, setting, methods

Cytoskeletal analysis was performed by embryo immunostaining with α-tubulin, γ-tubulin, acetylated-tubulin antibodies and DAPI or/ PI to visualise DNA. TEM analysis was carried out following embryo fixation in gluteraldehyde, incubation in osmium, aqueous uranyl acetate, dehydration through ethanol series, and immersion in Epon. Endometrial biopsies were fixed in gluteraldehyde solution and processed for SEM using standard methods. The study was conducted in an academic hospital with an IVF/PGD laboratory and 3 private IVF Units.

Main results and the role of chance

162 embryos were biopsied on day 3 for PGT-A (29 cycles), 10 cycles had no normal embryos for transfer, 30 normal embryos were transferred in 19 cycles leading to 12/19 (63.2%) +vehCG/ET and 11/19 (57.9%) Ongoing pregnancy rate/ET. 156 embryos were biopsied on day 3 for PGT-M (22 cycles), 2 cycles had no normal embryos for transfer, 34 normal or carrier embryos were transferred in 20 cycles leading to 15/20 (75.0%) +vehCG/ET and 13/20 Ongoing pregnancy rate/ET (65.0%). 152 embryos were biopsied on day 5 for PGT-A (37 cycles), 8 cycles had no normal embryos for transfer, 34 normal embryos were transferred in 29 cycles leading to 18/29 (62.1%) +vehCG/ET and 16/29 (55.2%) Ongoing pregnancy rate /ET. Analysis of endometrial biopsies with SEM revealed bacterial infections, inflammation and epithelial damage. So far, 33.3% of patients who received intracavitary infusions-antibiotic treatment per os achieved a +vehCG/ET in their next PGT-A/M cycle. Cytoskeletal analysis showed that the majority of spindles examined in both day3 and day5 biopsied embryos were normal (85/114(74.6%) and 87/137(63.5). However vitrification following day5 biopsy led to more cytoskeletal/ultrastructural anomalies which included multipolar/abnormally shaped spindles, chromosome-bridging, chromosome-lagging and more vacuoles, lipofuscins. and distension of mitochondria.

Limitations, reasons for caution

Patients undergoing PGT-A have various aetiologies (heterogeneous group). The embryos used for cytoskeletal and ultrastructural analysis in this study were all diagnosed with either chromosomal abnormalities or single gene defects following PGT-A or PGT-M.

Wider implications of the findings: This is the first study to compare implantation/pregnancy rates, cytoskeleton and ultrastructure of day5 vs day3 biopsied embryos. The similarities observed in implantation/pregnancy rates, and the limited ultrastuctural and cytoskeletal anomalies identified confirm the procedures’ safety and indicate in certain cases endometrial factors/inflammation responsible for failed implantation following PGT-A/M.

Trial registration number

Not applicable