If you’re preparing for a paternity test, you’re likely planning to test the DNA of the child and father in question. But there is also another important factor that must be included in the DNA paternity test, which can improve the probability of paternity. This is the DNA of the child’s biological mother.

You may ask, “If I’m testing for paternity, why is the biological mother’s DNA relevant?”

There are several reasons. Primarily, including the biological mother’s DNA on a paternity test helps to generate stronger test results and can explain failing test results and re-determine paternity.

As a brief overview, paternity tests check up to 17 genetic systems on the child and father, otherwise called markers or locations. In order to determine paternity, each marker must match in the father and child, except in the case of rare genetic mutations. Each matching marker is then assigned a number, called a relationship index. The higher the relationship index, the stronger the match.

After a relationship index is calculated for each gene marker, the indexes are multiplied to produce the Combined Paternity Index (CPI). The CPI is what ultimately determines paternity. CPIs that calculate at 99% or higher verify paternity, while CPIs at less than 99% show that the father is not actually the biological father of the child.

However, even if the father and child match at every gene marker, the CPI often falls under 99%, which can cause discrepancies in couples and families. Before making any decisions, families or individuals should re-test with the mother’s DNA, because it may completely improve the outcome of the paternity test and grant paternity to the father.

To explain, a CPI under 99% could show the mother’s genetic influence on the child and explain the gap in DNA between the child and father. By pinpointing which genetic factors come from the mother, and subsequently which come from the father, the overall CPI is raised to show the matches of DNA with the child and both parents.

There have been several paternity tests where the mother’s DNA has raised the probability of paternity to a 99.90%, which is a conclusive result showing that the father is really the biological father of the child. A mother’s DNA can also be used to verify other relationships – such as a grandparent or sibling DNA testing.

Including the mother’s DNA on a paternity or relationship test always shows strengthened test results and more accuracy for everyone involved. For more information about DNA paternity testing or a mother’s role in the process, please visit our Paternity DNA testing page.