Who's the father of my child?

Dear Alice,

I am not sure who the father of my son is. Is it possible to tell the father of the baby simply by knowing blood types and Rh factors of myself and the potential fathers?

Dear Reader,

Blood types and Rh (Rhesus) factors are used to determine the father's identity more often in fictional murder mysteries than in real life. Both blood types and Rh factors are inherited, so moms and dads of certain blood types and Rh factors can only produce children of certain blood types and Rh factors. For instance, two parents with type A blood cannot produce offspring with type B or AB blood, and two Rh-negative parents cannot have an Rh-positive child.

Since many folks have blood types and Rh factors in common, knowing these traits of both the mother and baby can only be used to eliminate certain people as possible fathers, but not to pinpoint a definite dad.

Paternity testing, which typically analyzes DNA (deoxyribonucleic acid — the carrier of genetic information) in blood or saliva, is the only method of definitively establishing biological parenthood, because DNA can be linked to a specific individual. DNA paternity testing is greater than 99 percent effective in both naming and eliminating possible dads.

Private laboratories offer at-home paternity test kits; a web search for paternity tests will provide you with scores of labs from which to choose. The tests are usually costly, and can yield results in 5 to 15 working days — the speedier the service, the more expensive. The test uses samples (either drops of blood or saliva from a cotton swab) taken from the child and possible father(s) to definitively determine if there's enough shared genetic material for one to be the biological child of the other.

Last updated Jul 20, 2015
Originally published Feb 16, 2001

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