The 70% failure rate of in vitro fertilization (IVF) treatments for human couples is thought to be the result of natural embryonic chromosomal abnormalities. UK researchers have attempted to tackle the problem by employing whole genome amplification (WGA) coupled with comparative genomic hybridization (CGH), providing the first comprehensive assessment of chromosome copy number in human embryos. CGH reveals the copy number of every chromosome segment >10 Mb in size, but requires 10,000 times the DNA of a single cell. The approach, described in Molecular Human Reproduction ( 6, 1055–1062, 2000), employs degenerate PCR to amplify sequences of interest in cells (blastomeres) from 3-day old embryos, and then single-cell CGH to detect genome wide amplifications/deletions using an equimolar mixture of normal and test cells. Not surprisingly, nine of the embryos contained cells with likely fatal chromosomal aberrations, ranging from multiple aneuploidy to partial deletions and their combinations. According to Wells, the next goal is “to reduce the length of time that the procedure requires and to optimize the protocol for clinical application.”