Infant mortality is a composite index which includes deaths of infants 0-1 weeks of age, namely neonates, and those of infants 7 days to 12 months of age. The causes of death in these two periods are characteristic and call for different modes of intervention. A new born baby is termed a neonate only if it shows life immediately after birth, otherwise it is termed a still-birth. In the neonatal period, deaths may be due to antenatal and birth causes. The single most important cause of neonatal deaths is prematurity and its related problems, followed closely by birth trauma, maternal diseases during pregnancy, congenital abnormalities (particularly neural tube and cardiac defects) and infections.
At levels of infant mortality in excess of 100 per 1000, about one third of the deaths occur in the neonatal period. At lower levels of infant mortality, neonatal deaths become very important and may account for 70% of infant deaths. The former is the situation in developing countries like Kenya, and the latter is the case in industrialized countries.