Although the components of litter size (ovulation rate, embryonic survival and uterine capacity) responsive to genetic selection are well established. However, the reality in existing “hyper-prolific” sows is that increased selection pressure for numbers born has led to indirect negative effects of intra-uterine crowding, reprogramming of fetal development, less efficient post-natal growth performance and adverse effects on carcass quality at slaughter. Therefore, a considerable amount of the variation in growth performance after birth may be pre-programmed during fetal development in the uterus (see Foxcroft and Town, 2004). The effects of prenatal programming on postnatal performance are not limited to effects on muscle development and growth. Harding et al. (2006) showed that the organs most notably affected by pre-natal programming in stillborn pigs with low birth weight were the heart, liver and spleen, with obvious implications for post-natal health outcomes generally. Both birth weight of the individual pig and between litter variation in birth weight are of considerable economic interest for pork production, as post-natal growth in the pre-weaning, nursery and grow-finish stages of production is impaired in low, compared with high, birth weight pigs (see review of Foxcroft et al., 2007). Available results indicate that pigs of low birth weight have poorer carcass and meat quality. Unfortunately, although selection for improved prolificacy has resulted in an increase of litter size at birth in most breeding populations, this has been associated with increased within-litter variation in piglet birth weight, as well as an overall decrease in average birth weight of the litter. The proportion of live-born vs. dead-born pigs within the litters of one population of hyper-prolific French sows suggests that the growth potential of the live-born pigs that survive to weaning will be seriously affected by intra-uterine competition with the increasing number of fetuses born dead. A better appreciation of the characteristics of prolific dam-lines is clearly needed. This information, and an increasing focus on the need to maximize total net revenues per sow in terms of the value of saleable pork products relative to the input costs involved per kg of pork sold, should drive the management of appropriate terminal dam-lines in the future. Ultimately, selection of sows with increased uterine capacity offers the best opportunity for increasing the number of pigs born per litter, without compromising the post-natal growth performance of these pigs. A comparison between the largest and smallest pigs within a litter has most frequently been used to study impacts of birth weight on postnatal growth performance. However, limitations in functional uterine capacity in hyper-prolific sows are predicted to result in prenatal programming effects on entire litters (Foxcroft et al., 2007). If this assumption is correct, then the origins of increasing variance in postnatal growth performance needs to be clarified as the basis for developing selection and production strategies that effectively address the problem. Innovative approaches to addressing the problems, as well as the opportunities presented by pre-natal programming of post-natal performance, will likely be the benchmark of the most profitable pork production systems in the next decade. In particular, these approaches will need to address the possible conflict between continued selection for hyper-prolificacy and increased variance in post-natal growth performance.