Buenos Aires has granted a family legal recognition of three parents.
A lesbian couple and the biological father of their child have all been listed on the child’s birth certificate, which gives them all legal recognition as parents of the child.
According the Registrar of Persons, Claudia Corrado, this is in the best interests of the child, and means the father, Hernan Melazzi, retains his rights and responsibilities for the child.
Mothers Susana Guichal and Valeria Gaete have been together for eleven years, and married for three.
They said they think of Mr Melazzi as more than just a sperm donor for their child.
Esteban Paulón, head of the LGBT Federation of Argentina told AFP: “We are so proud, on this historic day, of the decision of the Buenos Aires Provincial government.
“We didn’t even need to go to the courts.
“It is like science fiction for other countries, who are only just discussing equal marriage or common children.”
Mr Melazzi said: “This is a very important moment for the three of us and for Antonio, our child.”