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New figures have revealed women had fewer children than they expected and at an older age over the last two decades.
Between 1991 and 2007 women asked how many children they intended to have consistently gave a higher rate than the actual average fertility rate throughout that period.
The intended family size ranged between 2.0 and 2.16 children per woman when the actual fertility rate was around 0.3-0.4 children per woman lower until 2001.
Since then the gap between intended family size and overall fertility has narrowed.
In addition, between 1991 and 1994, childless women who said they would probably have a birth in the next 10 years were also asked at what age they expected to have their first child.
These findings were then compared with actual ages at first birth for a comparable sample of women ten years older in 2001/04.
Women expected, on average, to have their first child at a younger age than actually proved to be the case.
Women aged 22-25 in 1991/94 expected on average to have a child within 3.9 years - the actual average wait was 4.5 years.
For women aged 30-33, the anticipated two-year wait for a first child became 3.5 years on average.
Overall, the figures revealed there was a degree of uncertainty about fertility intentions for women throughout their childbearing years, including a significant minority of women who did not make firm decisions about future childbearing.
The study was undertaken by the Economic and Social Research Council (ESRC) Centre for Population Change at the University of Southampton and was published today in the Office for National Statistics (ONS) publication, Population Trends.