Los Angeles, July 25 (DPA) The perfect twins born earlier this month in Paris to the world's perfect couple, were no accident.

According to US Weekly magazine Thursday, Brad Pitt and Angelina Jolie used in-vitro fertilisation to conceive twins Vivienne and Knox.

A source close to the couple told the magazine that 'they both desperately wanted more babies soon', and says that the actress, 33, chose the $12,000 procedure so 'she wouldn't have to deal with the stress of trying to get pregnant. She could just knock it out'.

Jolie has often spoken of the couple's wish to raise a large family while they are still young, and in-vitro fertilisation improves the chances of conceiving twins from one percent to 25 percent.

Vivienne Marcheline and Knox Leon were born in France July 12. They joined adopted siblings Maddox, 6, Pax, 4, Zahara, 3, and the couple's biological daughter two year old Shiloh.