[Superfecundation and superfetation--the forgotten entities].

Superfecundation and superfetation are rare and obscure phenomena with no clear clinical significance but with legal and moral-social meanings. These obstetric rarities are known since the times of the ancient Greeks. There are several physiological explanations that account for superfecundation but not for superfetation, yet, both have been described. In this era of assisted reproductive techniques it is reasonable to assume that the prevalence of superfecundation increases, which may also apply to superfetation. Today, there are several reliable diagnostic techniques to verify heteropaternity in multifetal pregnancies, hence superfecundation. Nevertheless, our knowledge regarding these amazing phenomena remains limited due to both ethical and medico-legal barriers that prevent their implementation.