The human cleavage stage embryo is a cradle of chromosomal rearrangements.

The first cell cycles following in vitro fertilization (IVF) of human gametes are prone to chromosome instability. Many, but often not all, blastomeres of an embryo acquire a genetic makeup during cleavage that is not representative of the original zygotic genome. Whole chromosomes are missegregated, but also structural rearrangements of chromosomes do occur in human cleavage stage embryogenesis following IVF. Analysis of pre- and postnatal DNA samples indicates that the in vivo human conceptions also endure instability of chromosome number and structure during cleavage of the fertilized oocyte. This embryonic chromosome instability not necessarily undermines normal human development, but may lead to a spectrum of conditions, including loss of conception, genetic disease and genetic variation development. In this review, the structural instability of chromosomes during human cleavage stage embryogenesis is catalogued, channeled into etiologic models and linked to genomic profiles of healthy and diseased newborns.