Whoa, mama!

Expectant mom Kourtney Kardashian showed off her gorgeous, growing baby bump in a skintight white lace jumpsuit on Saturday night, hitting up Women's Health Magazine's Party Under the Stars with beau Scott Disick. The look, which is not a maternity style, is $475 from the brand Made for Pearl. 

A glowing Kardashian, 35, and Disick, 31, "looked very happy together" at the bash, held at Bridgehampton Tennis and Surf Club, a witness said. We're told neither drank alcohol -- Kourtney because she's pregnant and reformed party-boy Disick because he "wants to be a responsible father and boyfriend."

The couple has two children: 4-year-old son Mason and 2-year-old daughter Penelope. They've been in the Hamptons this summer filming "Kourtney and Khloe Take the Hamptons" with Kourt's sister Khloe Kardashian.