Human embryos with genetic defects may exhibit unusual cellular behaviour by the time they reach the four-cell stage, about 48 hours after fertilization.

Credit: SHAWN L. CHAVEZ

Renee Reijo Pera at Stanford University in California and her colleagues analysed the genetics of 45 single-celled embryos left over from in vitro fertilization procedures. About 75% of the embryos contained an abnormal number of chromosomes, with two carrying three copies of chromosome 21, which leads to Down syndrome. Time-lapse imaging revealed that normal embryos underwent precisely timed cell divisions, whereas 70% of embryos with abnormal chromosome counts did not. The researchers also observed that cells in abnormal embryos often fragmented into tiny pieces containing chromosomes (pictured).

Automated image tracking of cell division and fragmentation could provide a non-invasive tool to screen embryos for healthy in vitro fertilization candidates, the authors say.

Nature Commun. 3, 1251 (2012)