The limit of viability is the gestational age at which a prematurely born fetus/infant has a 50% chance of long-term survival outside its mother's womb. With the support of neonatal intensive care units, the limit of viability in the developed world has declined since 50 years ago, but has remained unchanged in the last 12 years.
Currently the limit of viability is considered to be around 24 weeks although the incidence of major disabilities remains high at this point.
 Neonatologists generally would not provide intensive care at 23 weeks, but would from 26 weeks.
During the past several decades, neonatal care has improved with advances in medical science, and therefore the limit of viability has moved earlier. As of 2006, the two youngest children to survive premature birth are thought to be James Elgin Gill (born on 20 May 1987 in Ottawa, Canada, at 21 weeks and 5 days gestational age), and Amillia Taylor (born on 24 October 2006 in Miami, Florida, at 21 weeks and 6 days gestational age). Both children were born just under 22 weeks from fertilization, or a few days past the midpoint of an average full-term pregnancy.
Amillia Taylor is also often cited as the most-premature baby. She was born on 24 October 2006 in Miami, Florida, at 21 weeks and 6 days gestation. At birth, she was 9 inches (22.86 cm) long and weighed 10 ounces (283 grams). She suffered digestive and respiratory problems, together with a brain hemorrhage. She was discharged from the Baptist Children's Hospital on 20 February 2007.