The development of the decidua in rodents is associated with the production of multinucleate and giant cells . In the rat, binucleate cells appear throughout the secondary or antimesometrial zone of the decidua by the eighth day of pregnancy , while in the mouse this region is characterized by large bi-, tri-, or tetranucleate cells . All decidual cells may eventually enlarge, containing nuclei of a size consistent with a DNA content of four, eight and possibly even higher multiples of the haploid complement . In the white rat spectrophotometric determination of DNA levels in decidual cells indicates that by the tenth day of gestation ploidy levels have reached 16C–32C, with maximal levels of 64 times the haploid DNA content . The mechanism of nuclear enlargement in decidual tissue is as yet unknown.