Although there is no sharp demarcation point, over time the limit of viability has become progressively lower, from a birth weight of 1,500g before 1940, to 1,000g and 28 weeks' gestation by the 1970s.(20) Survival is now common for infants of less than 750g and for those of 25 weeks' gestation. The lower limit of viability appears, at present, to be approximately 22–23 completed weeks of gestation, with survival and morbidity improving markedly with each later week of gestation. It is now governed by technological capacity, medical intervention, and the attitudes of the medical profession.(63, 66)