Can twins have different fathers?

Yes! Fraternal (DZ) twins develop when a woman releases two eggs instead of one during her monthly menstrual cycle. When this occurs and each egg is fertilized by sperm cells from the same man, DZ twins with the same father are created. While rare, it is possible that each egg could be fertilized by a sperm cell from two different men. This could happen as a result of separate acts of sexual intercourse that occur within the woman’s fertile period. DZ twins with different fathers would be created.

The term superfecundation means the fertilization of two (or more) eggs released during the same menstrual cycle by sperm from separate acts of sexual intercourse. A woman’s fertile period can last for five to seven days. So superfecundation that creates DZ twins with the same father may happen often.

But we can only know for sure that superfecundation happened when there is more than one father. When this occurs, it is called heteropaternal superfecundation (hetero = different; paternal = father). Although heteropaternal superfecundation is rare in humans, DNA paternity tests have shown that it does occur.

There are several examples of heteropaternal superfecundation in Greek mythology. For example, the twins Castor and Pollux were said to have different fathers. Pollux was the son of Zeus, and Castor was the son of a mortal man.

Twins with different fathers may also result from fertility treatments in which a mixture of sperm from more than one sperm donor is used.