Seven-years has traditionally been the time when love and affection give way to disillusion and disappointment.

But couples who manage to survive the seven-year itch would be wise not to get complacent.

The biggest threat to modern marriages actually comes from the 12-year itch, research has revealed.

The majority of couples who divorce have now spent more than a decade together before going their separate ways.

And they are increasingly likely to cite 'growing apart' or 'falling out of love' as the cause of their split.

There has been a four-fold increase in couples breaking up for these reasons in the last two years, amid increasing financial strain on families.

But infidelity is still responsible for more than a quarter of divorces. The seven-year itch - or the theory that adultery becomes impossible to resist after seven years - got its name from the 1950s film starring Marilyn Monroe.

The study by the Grant Thornton accountancy group, which was based on a survey of 90 of the country's biggest family law firms, echoed figures released last year which showed that marriages are most likely to fall apart around the 12-year mark.

Sally Longworth, of Grant Thornton's Forensic and Investigation Services, said: 'This rather dispels the age-old myth about marriages failing after seven years.

'It is impossible to put any scientific reasoning on why certain marriages succeed and others fail.'

(Read by Nelly Min. Nelly Min is a journalist at the China Daily Web site.)

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(Agencies)