Mortality from birth to adult life: a longitudinal study of twins

We have examined mortality from birth through adult life in a cohort of 2562 twins born in Birmingham, UK, between 1950 and 1954. Their birthweights and obstetric details had been recorded as part of a longitudinal study of births in Birmingham. There were a total of 151 perinatal deaths (perinatal mortality rate = 116 per 1000 births) and 227 infant deaths (infant mortality rate = 94 per 1000 live births). 70 deaths occurred after the age of one year. In comparison with national mortality rates in the UK, overall mortality in the twins was high (standard mortality rate, SMR = 259, 95% CI 221-300). Mortality was highest in the first year of life and, although it then declined progressively, it remained significantly higher that that of the general population until age 5 years. The excess mortality was largely due to conditions originating in the perinatal period but there were excess rates of congenital abnormalities, diseases of the respiratory system, digestive system and nervous and sensory organs. A Cox proportional Hazards analysis showed that the risk of death was related to low birthweight, prematurity and male sex. Death of the co-twin was highly predictive of mortality throughout the period of follow up. These studies not only underline the excess mortality associated with twin birth but show for the first time that this excess mortality extends into childhood.