Italy’s health ministry says it is launching an investigation into the error, which was only discovered when the woman was three months pregnant.

The mistake happened on December 4, when four couples with similar sounding names were receiving treatment at a specialist fertility unit at the Sandro Pertini Hospital in Rome, La Stampa newspaper reported.

There has been no word from the real mother of the twins, whose own IVF pregnancy reportedly ended with a miscarriage.

Health minister Beatrice Lorenzin said investigators would look at whether the hospital had “respected all the legal procedures” and expressed concern she had only learnt about the mistake through press reports.

“The national standards on assisted fertilisation, which are based on European directives, are very rigorous, and if applied correctly, guarantee the traceability of all biological material used in the reproduction process,” she said.

The local health authority in Rome said it only became aware there was a problem of “genetic incompatibility” between the parents and the embryos on March 27. It said it has halted all embryo implantations at the clinic until further notice.

The investigation will be led by geneticist Giuseppe Novelli and will look into whether there was any further mix-up of the embryos of two of the other women.

Michele Ambrosini, a lawyer representing the woman pregnant with twins, said she was determined to push on with her pregnancy.

Under Italian law the real mother of the twins has no chance of claiming custody of the children as whoever gives birth is the legal mother.

“Legal claims will be useless to get the twins back,” Lorenzo D’Avack, vice president of Italy’s national bioethics committee said.