However, this retrospective analysis does not account for the contribution of past migration to natural change –
mainly to births, given that migrants are mostly young, healthy individuals. The number of births over a given period
is determined both by the size and age structure of the female population and by fertility rates (i.e. the average
number of children per woman in each age group). Migration impacts on both factors – i.e. it affects the number
of women of childbearing age and, if migrant women have different fertility patterns, the total fertility rate of the
population as a whole. A recent ONS report (Dormon 2014) using the latest Census data for England and Wales
has shown that births to foreign-born women made up 25.5% of all births in 2011, up from 16.4% one decade
earlier (2001). However, this was mainly due to the increase in the number of foreign-born women of childbearing
age – total fertility rates of non-UK born women remained constant between 2001 and 2011 (2.21 in both years),
resulting in a decreasing gap with the fertility levels of UK-born women that increased from 1.56 to 1.84 over the
same period (Dormon 2014: 2). For a shorter period (2001-07) and for the UK as a whole, Tromans et al. (2009:
33) estimated the overall contribution of foreign-born women to the increase in the number of births at 65%. While
these figures point to the significant indirect contribution that immigration is making to UK population trends, it has