The pregnant actress hit the red carpet at Sunday's Screen Actors Guild Awards in Dior, wearing a beautiful, billowing white gown and dripping in Tiffany diamonds. The Jackie star dished on getting "really lucky" in finding -- and fitting into -- the dress.
"It just came off the runway last week and crazily fit," she told ET's Nancy O'Dell. "Shocking! It was very loose on the model."
Portman is expecting her second child with husband Benjamin Millepied after welcoming a son, Aleph, in 2011. But when it comes to their impending arrival, Portman revealed that the couple has yet to choose a name.
"You got to meet a baby before," she explained. "Gotta meet the baby and then figure it out."
Portman, who previously won a Screen Actors Guild Award in 2011 for her work on Black Swan, is nominated this year for her role as former First Lady Jackie Kennedy, in the film that follows her life after the assassination of President John F. Kennedy.
"I'm so proud of the film, Jackie, and to be here with the people I love working with," she said. "Especially at a moment that's dark in our country's history, to be celebrating art and people trying to express human emotion and be empathetic towards other people is good."