A very curious case happened in China. A man in fact asked for the DNA test before recognising the twins brought to light by his wife. The motivation? One of the two kids didn’t look like him at all. The test results left everyone amazed: the twins actually have two different fathers!

What happened is a very rare event. It is in fact a case of heteroparental superfecondation, described in the literature only for very few confirmed cases.

© REUTERS/Athit Perawongmetha/File Photo

Twin pregnancy

There are many ways for a twin birth to take place: in fact, we speak of mono zygotic and di-zygotic twins. These definitions refer to the mechanism that leads to the formation of the two embryos. In the first case, that of mono zygotic twins, a sperm fertilises an egg. After the formation of the zygote, the first cell agglomerate, this splits into two, leading to the formation of two individuals. These obviously share 100% of the genome.

The second case, the most common one, is represented by the di-zygotic twins. In this situation two different spermatozoa fertilise as many egg cells. The egg cell, in order to be fertilised, must be at a precise moment in its maturation cycle: ovulation must have occurred and the cell must be inside the Fallopian tubes. This time window is quite short and, generally, if a twin di-zygote pregnancy is established, the two egg cells are fertilised following the same sexual relationship.

The exceptions never fail

There are cases in which the egg cells are fertilised by sperm deriving from two coitus, separated by hours or at most one or two days apart. In this case the phenomenon is defined as super-fertilisation.
This is what happened in China. With the particularity that the woman’s partners were two. Precisely for this reason we speak of hetercaternal super-fertilisation. Very often these cases can be misunderstood since they can only be ascertained with the paternity test. Nature never stops surprising and offers curious phenomena… but this time the Chinese man must not have been very happy!