The happy trio, who reportedly have shared a bed for years and say they want to raise a child, took an oath of love in early October in the presence of Rio de Janeiro notary Fernanda de Freitas Leitao.
The lovers - a businesswoman and a dentist who are both 32 and a 34-year-old office manager - have been together for three years and wish to remain anonymous.
While these are the first women to enter a three-way civil union, a similar ceremony was held in 2012 for a man and two women in Sao Paulo state.
