Daily Mail: It has long been thought that a woman's decision to have children depends on her education.
But researchers say it's actually her personality that will determine when she becomes a mother.
And those who show concern for others are more likely to become young mothers, their study found.
Meanwhile, independent women with strong views are more likely to delay having a family and risk going through life childless.
The decision to postpone childbirth is driven by the same traits that make a woman choose an education and a career, it was found.
The Government-backed findings, based on records of 5,000 families over the past 20 years, come at a time of growing concern over the rising age at which women choose to become mothers and a boom in those having children in their forties.
Since the 1980s, the average age at which a British woman has her first baby has gone up from around 2 to over 30.
Mothers over 40 gave birth to 27,000 babies last year, three times the number of a decade ago, official figures show.
Almost one in five women are childless when they reach their late forties.
The study, paid for by the taxpayer-funded Economic and Social Research Council, said a minority of women who have put their careers ahead of family in their priorities have done the most to push up the age of childbearing.
Researcher Lara Patricio Tavares examined personality traits of mothers as recorded by the British Household Panel Survey.
She checked on whether mothers were agreeable, extrovert or neurotic - characteristics which mean they are more likely to be sympathetic to other people - or whether they showed more signs of being guided by conscientiousness and openness, qualities which mean they are more likely to be influenced by their own thinking and beliefs.
Dr Tavares found that being agreeable meant a woman would be altruistic and tender-minded.
'More agreeable women are more motivated to have a child and do it earlier.'
Open-minded people, however, are 'ready to question the conventions' and 'tend to believe that it is good to think for oneself'.
She added that they 'are less likely to be exclusively family-oriented. They might value their careers more and therefore face higher psychological childbearing costs.'
Open-minded women are more likely to choose a strong education. 'Personality traits influence both education and fertility decisions.'
Dr Tavares added that differences between childbearing choices were most obvious among well-educated women.
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