The Oscar-winning actress, debuted her growing baby bump in a Valentino gown at the Venice Film Festival premiere for her new film "Planetarium," reported People magazine.
The movie also stars up-and-coming model and actress Lily-Rose Depp.
Millepied and Portman, 35, got married in 2012 in Big Sur, California.
The couple are already parents to five-year-old son Aleph.