Microarray analysis reveals abnormal chromosomal complements in over 70% of 14 normally developing human embryos.

STUDY QUESTION: What are the aneuploidy rates and incidence of mosaicism in good-quality human preimplantation embryos.

SUMMARY ANSWER: High-level mosaicism and structural aberrations are not restricted to arrested or poorly developing embryos but are also common in good-quality IVF embryos.

WHAT IS KNOWN ALREADY: Humans, compared with other mammals, have a poor fertility rate, and even IVF treatments have a relatively low success rate. It is known that human gametes and early preimplantation embryos carry chromosomal abnormalities that are thought to lower their developmental potential.

STUDY DESIGN, SIZE AND DURATION: The embryos studied came from nine young (age <35 years old) IVF patients and were part of a cohort of embryos that all resulted in healthy births. These 14 embryos inseminated by ICSI and cryopreserved on Day 2 of development were thawed, cultured overnight and allowed to succumb by being left at room temperature for 24 h. Following removal of the zona pellucida, blastomeres were disaggregated and collected.

PARTICIPANTS/MATERIALS, SETTING AND METHODS: There were 91 single blastomeres collected and amplified by multiple displacement amplification. Array-comparative genomic hybridization was performed on the amplified DNA. Array-data were normalized and aneuploidy was detected by the circular binary segmentation method.

MAIN RESULTS AND THE ROLE OF CHANCE: The good-quality embryos exhibited high rates of aneuploidy, 10 of 14 (71.4%) of the embryos being mosaic. While none of the embryos had the same aneuploidy pattern in all cells, 4 of 14 (28.6%) were uniformly diploid. Of the 70 analysed blastomeres, 55.7% were diploid and 44.3% had chromosomal abnormalities, while 29% of the abnormal cells carried structural aberrations.

WIDER IMPLICATIONS OF THE FINDINGS: Finding such a high rate of aneuploidy and mosaicism in excellent quality embryos from cycles with a high implantation rate warrants further research on the origin and significance of chromosomal abnormalities in human preimplantation embryos.

STUDY FUNDING/COMPETING INTEREST(S): This research was supported by the Instituut voor de aanmoediging van innovatie door Wetenschap en Technologie in Vlaanderen (IWT-Vlaanderen). A.M. is a PhD student at the IWT-Vlaanderen. C.S. is a postdoctoral fellow at the FWO Vlaanderen. There are no competing interests.