A comparative analysis of the south-american legal systems on law of succession, and inheritance rights of unborn sons or super-posthumous children. The devolution of property on an heir or heirs upon the death of the owner hits the problem of assisted reproductive technologies, assisted fertilization in suppositions of predecease of the sperm donor in married or not married couples. The article considers legal requirements statued for the hability for becoming heir, and if the expression of consent of the man (donor of the genetic material), and the documents where he can express his will, allowing the post-mortem implantation of cryopreservated embryos or in vivo or in vitro fertilisation can be equivalent to a last will or testament. The work raises the necessary reforms to make these new realities possible.