Developmental ability of chromosomally abnormal human embryos to develop to the blastocyst stage

TLDR

Morphology and developmental competence correlate with chromosome abnormalities, yet absolute correlations are rare, making embryo selection a difficult task in assisted reproduction. The study aimed to identify which chromosomal abnormalities allow development to the blastocyst stage. Chromosomally abnormal embryos identified by PGD were cultured to day 5–6, monitored daily, and after extended culture fixed and analyzed by two rounds of FISH using the same probes as PGD. Trisomic embryos reached the blastocyst stage in 37 % of cases, extensive mosaicism was observed, and only monosomies compatible with first‑trimester development (X and 21) were detected at blastocyst stage, indicating that extended culture cannot reliably exclude clinically relevant trisomies.

Abstract

A correlation between morphology, developmental competence and chromosome abnormalities is established. However, since absolute correlations are rare, embryo selection remains one of the most arduous tasks in assisted reproduction. This study was undertaken in order to determine which chromosomal abnormalities are compatible with development to the blastocyst stage.Embryos diagnosed by preimplantation genetic diagnosis (PGD) as chromosomally abnormal or unsuitable for transfer were cultured to day 5 or 6. Morphology and development were observed daily. After extended culture, embryos were fixed and analysed by two rounds of FISH with the same probes used for PGD.Some types of numerical chromosome abnormalities do not preclude full differentiation in vitro. For instance, extensive mosaicism was detected in blastocysts and trisomic embryos reached the blastocyst stage with a frequency of 37%. Interestingly, only those monosomies compatible with first trimester development (monosomy X and 21) were detected at blastocyst stage.Even though there is a strong selection against chromosomally abnormal embryos, extended culture to day 5 or 6 cannot be used as a reliable tool to select against clinically relevant chromosome abnormalities such as trisomies.