ANGELINA JOLIE and partner BRAD PITT used fertility treatments to conceive their newborn twins, a new report has suggested.

The couple was desperate to quickly expand their brood - and turned to artificial insemination so they wouldn't have to "deal with the stress" of trying to get pregnant, reports US magazine US Weekly.

And that could be why they have a double bundle of joy - the chances of a 33-year-old woman like the Wanted star having fraternal twins naturally are fewer than one per cent, while with IVF the likelihood raises to one in four, according to the publication

A source says: "They conceived through in vitro fertilisation. They both desperately wanted more babies soon."
"Things were so hectic with their filming schedules and the kids, the simply didn't have time to keep trying. They were too impatient."

Last year, the Tomb Raider star told UK magazine Elle: "If we're going to have 10 kids, we'd like to raise them while we're young."

Fraternal twins Knox Leon and Vivienne Marcheline - born this month in Nice, France - became the fifth and six children to join the Pitt-Jolie clan of Maddox, six, Pax, four, Zahara, three, and biological daughter Shiloh, two.