The Perinatal age is that phase in human development from the time the embryo has just achieved the stage of 'independent' existence to the first week of life after birth, whatever the gestation at delivery.

The Age of Viability has been advancing relentlessly as medical revolution continues to unfold. Whereas it used to be 28 weeks, this has been brought back to as much as 23 weeks [22 weeks in a few countries]. Unfortunately, there has been a profound increase in morbidity and mortality associated with the increased survival to the extent it has led some to question the ethics and morality of resuscitating at the edge of viability. How far back can we push the boundary between intruterine and extrauterine gestation is anyone's guess.

Phases of the Continuum

Embryo

Fetus

Neonate

Infant

Preterm infant

Term infant

Postterm infant