Glujovsky D, Shamonki M and Bergh P. 2007. Fertility and Sterility by American Society for Reproductive Medicine. Adjusting for all analyzed variables, only initial gestational sac count, age, and body mass index were associated with the spontaneous embryo reduction rate. Twins had a lower chance of having a spontaneous embryo reduction than singletons. When only spontaneous single embryo reduction was assessed, women with two or three initial gestational sacs were less prone to have a spontaneous single embryo reduction than women with one initial gestational sac.