Angelina Jolie is on a special diet to help her get pregnant.

The 'Changeling' actress, who already raises six children with her partner Brad Pitt, has reportedly taken several steps to ensure she is expecting again by the summer.

A source said: "Angelina is doing everything she can to get pregnant. She is taking prenatal vitamins, has dramatically cut down on her junk-food consumption, and is seeing her obstetrician regularly whenever she's back in Los Angeles."

It has been claimed doctors previously advised Angelina against trying for another baby for a year after her twins Knox and Vivienne were born last July.

The 33-year-old star is determined to follow her strict schedule and conceive again as soon as the 12 months have passed.

The source added to America's OK! magazine: "Her goal is to be pregnant by the time Knox and Vivienne have their first birthday. Angelina is one of those people who always manages to achieve whatever she wants."

Along with their twins, Angelina and Brad also have three adopted children - seven-year-old Maddox, Pax, five, and Zahara, four - as well as a two-year-old biological daughter Shiloh.

Brad, 45, recently revealed the couple were considering extending their brood in the near future. He joked: "We average about two a year, so I guess we're overdue, aren't we?"