Women are having children later in life because they are spending longer in education , new research claimed today.
Academics from the University of Southampton looked at women in Britain and France and found that finishing full-time education and training at an older average age is the main reason why people are having their first child later in life.
Professor Maire Ni Bhrolchain, who conducted the study with Dr Eva Beaujouan, said: ''Later childbearing has been a major feature of fertility trends in recent decades, both in Britain and other developed countries.
''A large number of explanations have been suggested for the trend towards later parenthood, but our study is the first to show that the major influencing factor is that people have been staying on longer in education and training.''
The average age of a woman having her first child in 2004 was 27, three years later than in 1974, when the average age was 24, the researchers said.
During these three decades, young men and woman were progressively staying longer at school and also going into further and higher education in greater numbers - with women completing their education or training at an increasingly later age.
In the late 1970s, young women were leaving full-time education or training at an average age of 18, but by 2004 this had risen by two years to an average age of 20.
''The data we have examined shows that, in the past several decades, young people have been starting their full adult lives around two years later on average than in the recent past and this has meant family life starting later too,'' said Professor Ni Bhrolchain.
The Southampton study focused on the period between the early 1980s and the late 1990s, during which time the mean age of women having their first birth rose by almost one-and-a-half years.
During the same period, the time between women leaving full-time education and a first birth rose by only 0.6 years. This means that about three-fifths of the change in age at first birth in Britain is due to more time being spent in education and training. The figure is four-fifths in France.
So longer education and training is the most important explanation for later childbearing, although not the only one. There are other contributory factors, the study claimed.
Professor Ni Bhrolchain said: ''If we start the clock when young women leave full-time education or training, the delay to motherhood, compared across the decades, is much less than looking purely at the differences in their ages at their first birth.''
To investigate the study, the researchers compiled and analysed data in Britain from the General Household Survey and in France from the Family History Survey.
The study, called Fertility Postponement, is largely due to rising educational enrolment, is published in the journal Population Studies.