Angelina Jolie wasn't knocked up with twins by way of Brad Pitt's penis. Instead, she went with in vitro fertilization because nobody puts Angelina in a corner, not even nature! Unless nature looks like Billy Bob Thornton then maybe. Us Weekly reports:

"They conceived through in vitro fertilization," a well-placed source within their camp tells Us. "They both desperately wanted more babies soon."
The chance of having fraternal twins at Angelina's age (33) naturally is under 1 percent; with in vitro, the chances are 25 percent.
The actress chose the procedure (which can cost around $12,000 a pop) so "she wouldn't have to deal with the stress of trying to get pregnant," the source tells Us. "She could just knock it out."

Wow. Is Brad Pitt even having sex with Angelina Jolie? Or is he locked in a room every night with a copy of Gia and some test tubes? Some guys have all the luck.
(Source)