The World Health Organization defines perinatal mortality as the "number of stillbirths and deaths in the first week of life per 1,000 total births, the perinatal period commences at 22 completed weeks (154 days) of gestation, and ends seven completed days after birth", but other definitions have been used.

The UK figure is about 8 per 1,000 and varies markedly by social class, with the highest rates seen in Asian women. Globally, an estimated 2.6 million neonates died in 2013 before the first month of age,