Two gay Italian women on Friday won the right to adopt each other's children in a legal first.

All previous verdicts in Italy in favour of lesbian women being legally recognised as the parents of their partner's children are at the appeal stages.

In its definitive sentence, Rome's juvenile court said Marilena Grassadonia, president of the Rainbow Families association, could adopt her wife's twin boys. In turn, her partner adopted Grossadonia's son. All three were conceived by artificial insemination.

In March, a man won his request to adopt his partner's child, but rights watchers believed the ruling may have slipped through the net due to an administrative error, with the office of the prosecutor in charge of the case failing to file an appeal in time.

Grassadonia was a vocal campaigner in Italy during the heated debate earlier this year over a contested civil unions bill.

The text, adopted by parliament's upper house after a clause allowing gay couples to adopt their parnters' biological children was removed, will be examined by the lower house from May 9.

Italy's Prime Minister Matteo Renzi has said he will resort to a confidence vote on the government, if necessary, to make the bill law.

While they wait for the law, courts have been finding in favour of gay couples since 2014 based on current legislation which favours "emotional continuity" for children.

"On a personal level, it's a huge satisfaction, but I cannot be fully happy when I think that our (Rainbow) families depend on individual decisions" by courts, rather than having their rights enshrined in law, Grassadonia said in a statement Friday.

Gay watchers said the bill had been watered down under pressure from the right in a country which boasts the Vatican in its midst.

Massimo Gandolfini, who campaigned actively against the civil unions bill and organised a "Family Day" of Catholics in the capital city in protest in January, was received by Pope Francis in the tiny city state of Friday.

"He encouraged me to keep going, and we agreed Italy had to be a polar star in the middle of this disaster that is destroying humanity and the family," Gandolfini told AFP.