Paternity tests in California give a relatively straightforward answer, i.e., the man is either the biological father of the child or not. Sometimes, the result of twins is a surprise, showing two different fathers. It is rare but having twins with different fathers is not unusual.
How it happens
Scientifically, when the woman’s egg becomes fertilized, their body changes to prepare for pregnancy. One of the things that happen is egg forms a thick outer coating known as “zona pellucida,” which prevents other sperm from fertilizing the egg. However, there are unique circumstances where two eggs release and become fertilized by two different men’s sperm, leading to twins being born with different fathers. This situation is known as “heteropaternal superfecundation.”
This phenomenon, referred to as superfetation, occurs when a woman releases another egg into her reproductive system days or even weeks after ovulation. Another possibility is when the zona pellucida surrounding one of the eggs is weaker than usual. In this case, another man’s sperm can penetrate the egg and fertilize it with the first man’s sperm.
While dual egg fertilization scenarios are rare, they are not impossible. There are a few documented cases of twins with different fathers. The most famous case is of a mother of twins in Texas who acknowledged that she had an affair when she conceived her twins. A paternity test confirmed that her fiancée was indeed the father of one of the twins, but the other child belonged to the man with whom she had an affair.
This phenomenon places parents in a unique legal situation. For example, in California, if a man’s name is not on the birth certificate, he is not legally responsible for child support. However, suppose paternity tests later prove that he is indeed the child’s father. In that case, he can be retroactively held responsible for child support payments and have some legal rights over his child’s welfare.