In the context of the present session, we intend to summarize existing literature that indicates that the variation in growth performance after birth may be largely determined, and essentially pre-programmed, during fetal development in the uterus. Furthermore, it is likely that these pre-programmed limitations in growth performance will only finally express themselves in the late grower / early finisher stage of production. We will also present preliminary evidence that differences in fetal development that will likely affect postnatal growth performance can even be present without associated effects in birth weight. Thus sorting pigs by weight at the nursery and grower stages will not resolve the variation in growth performance that is still an inherent characteristic of particular pigs or litters. Thus we face the conundrum that 13 pigs born in two different litters, with the same average birthweight, may originate from litters with very different numbers of surviving embryos around day 30 of gestation, and this will pre-program these two litters to have very different postnatal growth potential.