Hello Doc, Is there any way of determining the father of a child before it is born?

Having a baby is a lifelong responsibility and hopefully an even greater reward -- for somebody! As a mother's belly swells, she knows with deep certainty that the child is hers. Each time the baby moves or kicks, the bond between her and her child grows.

Depending on the situation, the father may be pretty sure that the child is his. For most of history, though, dads have had to rely on circumstantial evidence as the foundation on which to build this crucial relationship. After the baby was born, he could feel more sure he was the dad if the baby looked like him ("He has your feet, Honey!"), but often these early resemblances are at least partially creative imaginations.

In 1901 biologist Karl Landsteiner distinguished between three types of blood -- groups A, B, and O. A fourth group -- AB -- was discovered a year later by another research team. As the inheritance patterns of these blood groups were worked out over the next decades, it became possible to use blood tests to exclude some men from being the fathers of some children. For instance, if the parents both have blood type O, then the children must all have blood type O. If a child were to have blood type A, B, or AB, then the presumed father must not be the real father. If the child's blood type were O, then the presumed father might be the real father -- but so might millions of other men. Here is a list of possible and impossible situations:

These are general rules, though, and exceptions apply. Very rarely, gene mutations may change the rules such that “impossible children” become possible.