The placenta is critical for nourishing the fetus throughout pregnancy, and also produces hormones that alter the metabolic functions of the mother. While the effects of nutrition on fetal development and long-term outcome have been very well documented, there are only a few reports based on studies in rat, sheep, and guinea pigs on how specific nutrients or general nutritional status affect the development of the blastocyst, its implantation, and the subsequent placenta. The data suggest that placental development is highly adaptable and that many types of compensation are possible for suboptimal nutrition