Research suggests that, as cases of teenage pregnancies, sexual infidelity and multiple partners increase, 1 in 25 fathers could unknowingly be raising another man’s child.

With improvements in genetic testing, thousands of fathers every year are discovering that “their” child is someone else’s. A study by scientists from Liverpool John Moores University concludes that 4 per cent of all men are unwittingly bringing up a child they have not fathered.

Of the men who demand a paternity test because they suspect infidelity, one in four have their suspicions confirmed.

The team gives warning that the trend, known as “paternal discrepancy”, poses serious implications for the future of the family.

Paternity tests have also featured in high-profile disputes involving celebrities and politicians. This year David Blunkett, the Secretary of State for Work and Pensions, learnt that he was not the father of the latest child of his former lover, Kimberly Quinn. Liz Hurley won child support for her son Damian after tests proved that Steve Bing, a millionaire television producer, was his father.

Recent scientific advances have resulted in a boom in the use of DNA profiling and genetic testing, which is relied on in areas such as organ donation and criminal investigations. They are also being used by a growing number of men keen to have access to a child or to disprove a claim for child support made against them.

An estimated 10,000 paternity tests are carried out each year. While many of the checks are conducted under the scrutiny of the Child Support Agency (CSA) or the courts, there are an increasing number of internet DNA-testing sevices available.

The researchers, led by Mark Bellis, of the Centre for Public Health at Liverpool, analysed a wide range of international studies, looking at estimates of paternal discrepancy between 1950 and 2004.

Their findings, published in the Journal of Epidemiology and Community Health, show that rates of cases where a father was not the biological father of his child ranged from 1 per cent in some studies to as many as 30 per cent. Experts generally agree that the rate is below 10 per cent. The Liverpool team said that their meta-analysis suggests a 4 per cent rate, meaning that about one in 25 families could be affected.

“For any father, identifying that the child they are raising as their biological progeny is actually sired by another man can have substantial health consequences,” the researchers said.

“Such knowledge can also destroy families, affecting the health of the child and mother as well as that of any man who is ultimately identified as the biological parent.” Suspected infidelity, as a result of a man finding out that a child is not his own, can lead to domestic violence against women.

While genetic tests once involved blood samples being extracted by a syringe, they can now be carried out using strands of hair or a mouth swab sent to laboratories by post.

“Modern genetic techniques continue to open a Pandora’s box on hitherto hidden aspects of human sexual behaviour,” the reserachers conclude. “No clear population measures of paternal discrepancy are currently available.

“However, recent trends in sexual health suggest unprotected sex and multiple partners are comparatively common occurrences with a large proportion of conceptions still unplanned.”

The researchers said that in a society where services and life decisions were increasingly influenced by genetics, this difficult issue could not be ignored.

Given the researchers’ findings, it might be better for all concerned if they choose to remain in the dark about any “suspicious” children.

HOW TO CHECK OUT FATHERHOOD

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