Babies registered jointly by unmarried parents have a 35 per cent higher chance of dying before their first birthday than those of married parents with fathers of the same social class.
Between 1988 and 1990, the infant mortality rates in England and Wales for babies registered by both parents living at different addresses was 11 per thousand live births, and for unmarried parents living together it was 9.8. This compares with a rate of 7.3 for babies born to married parents.
The statistics are significant because the conventional wisdom has been that registration of a birth by both parents indicates a stable environment - as advantageous as having married parents.
In 1990, a total of 28.3 per cent of all live births occurred outside marriage, compared with 27 per cent in 1989 and 12.8 per cent in 1981.
The figures, for 1988-90, also show that babies of unmarried parents are 2 to 3 per cent lighter than those of married parents across all social classes. This may partly explain the different survival rates, argues the study.
An infant's chance of survival is closely associated with its birth weight. In the three years 1988 to 1990, nearly half of all babies under 2lb3oz (1kg) died within a month, compared with just one in every 1,000 babies weighing 6lb9oz (3kg) or more.
Mortality statistics 1990, perinatal and infant: social and biological factors (Series DH3 No 24); HMSO; pounds 10.10.Reuse content