While Yorkshire fetal growth appears to depend on increasing placental size, more extensive vascularization of a smaller placenta appears to support Meishan fetal growth. Further studies are needed to extend our knowledge of the mechanisms controlling placental growth and vascularization. The ability to manipulate conceptus size may allow producers the opportunity to increase litter size in domestic pigs. More piglets farrowed per sow per year combined with the effects of fetal genotype on postpartum growth rate, as confirmed by the current study, would allow more efficient pork production