Can twins have different fathers?

In rare cases, fraternal twins can be born from two different fathers in a phenomenon called heteropaternal superfecundation. Although uncommon, rare cases have been documented where a woman is pregnant by two different men at the same time. In order to figure out if this is the case, a DNA paternity test can be done after the birth of the twins. A DNA paternity test can also be done while the woman is pregnant in order to determine if the twins have different fathers.

Twins with different fathers: is it common?

When it comes to twins, the image that probably comes into your mind is identical twins – which is when a single egg that has been fertilized by a single sperm is split. It's impossible for these types of twins to have different fathers.

However, fraternal twins – when two separate eggs are fertilized by two separate sperm – can look different from one another. Only about 20 Heteroptenal superfecundation cases worldwide have been reported to date. So, while it's not common, it's definitely possible for twins to have different fathers in a phenomenon called heteropaternal superfecundation.

How heteropaternal superfecundation occurs

Heteropaternal superfecundation, or when twins have different fathers, is actually extremely rare. It occurs when a second egg is released during the same menstrual cycle. That egg then needs to be fertilized by the sperm of a different man during sex that takes place in a short period of time from the time that the first egg was fertilized.

Basically, in order for this to happen, a woman needs to release an egg, have sex with a man, then release another egg, and have sex with another man – all within her ovulation window, which is 12-24 hours from the release of an egg. However, since sperm can live in the body for roughly five days, the timeline can be extended.

Paternity testing after twins are born

Fraternal twins already look different from one another, since they are born from two different eggs fertilized with two different sperm, so there's no quick way to determine if they are from different fathers. However, one way to figure out if twins have different fathers is with a paternity test after the twins are born.

A DNA paternity test, which will determine if a man is a child's biological father, can be done quite easily after the twins are born in one of two ways. The test can be either a blood test or a cheek swab and it must be done for both twins and the fathers in question. A lab will then run the tests and confirm who the father is – and whether the twins have different fathers.

Prenatal paternity testing

Amniocentesis and CVS are two invasive prenatal tests that are almost never performed for paternity testing. If they are performed for another indication, you may discuss adding paternity testing to the analysis. Invasive tests may increase the risk of miscarriage.

A non-invasive prenatal paternity (NIPP) test requires taking the mom-to-be's blood during the first trimester and then having the lab analyze the fetal DNA. You will also need to get DNA from the potential fathers though a cheek sample as mentioned above.