Viability
Viability refers to a point in fetal development at which the fetus may survive outside the womb. The lower limit of viability is approximately five months gestational age, and usually later.
There is no sharp limit of development, age, or weight at which a fetus automatically becomes viable. According to data years 2003-2005, 20 to 35 percent of babies born at 23 weeks of gestation survive, while 50 to 70 percent of babies born at 24 to 25 weeks, and more than 90 percent born at 26 to 27 weeks, survive. It is rare for a baby weighing less than 500 gm to survive.
When such babies are born, the main causes of perinatal mortality are that the respiratory system and the central nervous system are not completely differentiated. If given expert postnatal care, some fetuses weighing less than 500 gm may survive, and are referred to as extremely low birth weight or immature infants. Preterm birth is the most common cause of perinatal mortality, causing almost 30 percent of neonatal deaths.
Read more about this topic: Fetus