Viablity is the point at which the fetus becomes viable, that is potentionally able to live outside the mothers womb albeit with artificial aid. The age of viability appears to be between 23 and 24 weeks of gestation corresponding to fetal lung developement, the respiratory system is probably the last to achieve functional maturity. 24 weeks of gestation finished (24 + 0) is the lower limit of vialibity in the Czech republic since 1994.