Proportion of incorrectly established paternities has decreased over time, study finds

Determining who is the biological father of a child is a sensitive subject, but the answer can be crucial in important issues. In a nationwide study published in the Journal of Internal Medicine, researchers from Karolinska Institutet, by using two different models, have been able to show that the proportion of incorrectly established paternities in Sweden is as low as 1.7 percent, a figure that has decreased over time.

The genetic link between a father and a child is an eternal question which, for obvious reasons, can often be difficult to determine. However, with the discovery of blood groups at the beginning of the 20th century and how these are inherited, it has been possible to obtain a reliable answer in some individual cases."

Gustaf Edgren, Researcher, Department of Medicine, Solna, Karolinska Institutet

An incorrectly attributed paternity, where a man is wrongly believed to be the genetic father of a child, can have consequences both for the family in question, but also for society at large.

Inheritance disputes and order of succession are assessed on the basis of biological parenthood, and in medical research and healthcare, correct knowledge of biological kinship can be of central importance.

Based on previous studies with selected groups, the frequency of misattributed paternity has been estimated to be as high as 20 to 30 percent.

"However, there has been a lack of research that has studied this in a reliable and therefore meaningful manner," says Gustaf Edgren.

In this new study, researchers at Karolinska Institutet linked two different registers: a transfusion database containing blood group data and the Swedish multigenerational register containing detailed information on kinship, for example, who is registered as the mother and father.

Based on children born between 1930 and 2010, nearly two million so-called family units were created with information on the blood type of the mother, father, and child.

"To analyze these data, we used two independent statistical methods, to ensure the results," explains Gustaf Edgren.

The first method examined all blood group combinations that are genetically impossible if there is to be biological compliance. One such example is that both parents have blood type O, while the child has a different blood type.

Using the second method, the research group instead proceeded from a distribution of blood groups and examined both impossible and possible blood group combinations for the child.

"Both methods yielded the same results, where the incidence of incorrectly established paternities was an average of 1.7 percent. This shows that the frequency is significantly lower than in many previous studies," says Gustaf Edgren.

The research results are also consistent with other Western European studies, including Dutch and Flemish genealogy materials where the estimated incidence of incorrectly established paternity is between one and two per cent.

The study also shows that the number of incorrectly established paternities was higher in the 1930s, with a figure of about three percent - a figure that has decreased gradually over the years.

"If we look at the latter part of the 20th century, the number drops to about one percent. Why exactly is difficult to say, but one hypothesis is that we now have better and more accessible contraceptives. Society has also changed, for example, in the past divorce was not as acceptable", says Gustaf Edgren.

The study also shows that incorrectly established paternity is more common among parents with a shorter education.

The findings fill a scientific knowledge gap and further contribute to our understanding of population genetics and social structures.

"The presence of incorrectly determined paternity is lower than we expected and is important, for example, for everyone working with the Swedish multigenerational register. This knowledge provides an understanding of family relationships and forms a good basis for discussion in genetic counselling, but it is also useful for an evolutionary understanding in sociology," concludes Gustaf Edgren.