Spatial Distribution of Aneuploidy in Human Blastocysts and the Representativeness of Trophectoderm Biopsy Assessed by iFISH

Christensen, Cecilie Thybo

4. term

Biotechnology, Master

2026

2026-06-01

71

Infertility affects about one in six people of reproductive age. As a result, medical assistance such as in vitro fertilization (IVF) is increasingly used. Despite major advances, failed implantation and early pregnancy loss remain common. A key reason is abnormal numbers of chromosomes in the earliest embryos (blastocysts). Aneuploidy means cells have too few or too many chromosomes. It arises from errors during cell division and can lead to either uniformly aneuploid embryos or mosaicism, where some cells are normal and others are not. Mosaicism complicates preimplantation genetic testing for aneuploidy (PGT-A), because a small biopsy may not reflect the chromosomal makeup of the whole blastocyst. This creates clinical and ethical dilemmas if embryos are discarded even though they might still develop into a healthy baby. This study set out to examine how chromosomes are distributed in cells and early embryos. We used fluorescence in situ hybridization (iFISH), a lab method that makes specific chromosomes light up, to map chromosomes 11 and 21 in cultured SH-SY5Y and HeLa cells. The method worked reliably in these cell lines. We then adapted the protocol to human blastocysts, but it did not produce interpretable data in that context. Therefore, we cannot draw conclusions about mosaicism or changes in chromosome copy number in blastocysts from this work. However, the study establishes a methodological foundation for future research on chromosome positioning and organization in early human development.

Ufrivillig barnløshed rammer cirka én ud af seks personer i den reproduktive alder. Derfor bruger man i stigende grad medicinsk assisteret reproduktion som for eksempel in vitro-fertilisering (IVF). Trods store fremskridt er manglende implantation af embryoet og tidlige graviditetstab stadig almindelige. En vigtig forklaring er fejl i antallet af kromosomer i de tidligste embryoner (blastocyster). Aneuploidi betyder, at celler har for få eller for mange kromosomer. Det opstår ved fejl i celledelinger og kan give enten ensartede aneuploide embryoner eller såkaldt mosaikisme, hvor nogle celler er normale og andre ikke. Mosaikisme gør præimplantations genetisk testning for aneuploidi (PGT-A) vanskelig, fordi en lille vævsprøve ikke nødvendigvis afspejler hele blastocystens kromosomsammensætning. Det skaber kliniske og etiske dilemmaer, hvis embryoner frasorteres, selv om de måske kunne udvikle sig til et raskt barn. I dette studie ville vi undersøge, hvordan kromosomer er fordelt i celler og i tidlige embryoner. Vi brugte fluorescens in situ-hybridisering (iFISH), en laboratorieteknik der får bestemte kromosomer til at lyse op, til at kortlægge kromosom 11 og 21 i dyrkede SH-SY5Y- og HeLa-celler. Metoden virkede stabilt i disse cellelinjer. Vi tilpassede derefter protokollen til humane blastocyster, men her gav den ikke fortolkelige data. Derfor kan vi ikke konkludere noget om mosaikisme eller ændringer i antallet af kromosomkopier i blastocyster på baggrund af dette arbejde. Til gengæld etablerer studiet et metodisk udgangspunkt for fremtidige undersøgelser af kromosomers placering og organisation i den tidlige menneskelige udvikling.

[This apstract has been rewritten with the help of AI based on the project's original abstract]

Mosaik ; Humane blastocyster ; iFISH ; PGT-A ; Fertilitet ; PGT ; Trofektoderm ; Indercellemasse ; Aneuploidi

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