Abnormal offspring syndrome (AOS), also known as large offspring syndrome, is characterized by overgrowth, limb hyperflexion, abdominal wall defects, umbilical hernia, hardened umbilicus, open urachus, gelatinous material in the peritoneal cavity, hepatic cysts, abdominal ascites, hemorrhage, enlarged heart, kidney, lung, pancreas, and tongue, organ and skull asymmetry, and increase in the length of long bone. Published results suggest that the effect of IVP on birth weight is independent of the culture medium, the bull, or the breed, suggesting that molecular mechanisms beyond those at the DNA sequence level are at play in this phenomenon. In this review, we present the current knowledge about AOS, from its putative inception prior to embryo transfer through pregnancy and parturition, as well as the clinical findings relating to this condition. We and others have demonstrated that AOS is an epigenetic syndrome, and in this chapter, we summarize those findings. Lastly, we discuss the possibilities of early identification during pregnancy.