The WHO defines the perinatal period as "The perinatal period commences at 22 completed weeks (154 days) of gestation and ends seven completed days after birth." Perinatal mortality is the death of fetuses or neonates during the perinatal period. A 2013 study found that "While only a small proportion of births occur before 24 completed weeks of gestation (about 1 per 1000), survival is rare and most of them are either fetal deaths or live births followed by a neonatal death."