Blake Lively looked absolutely fabulous when she stepped out for L’Oreal Paris’ Women of Worth Celebration in New York City Tuesday night.

The pregnant actress donned a backless gown to the event held at the Pierre Hotel. Lively, 27, accompanied Brittany Wenger, a 19-year-old who, at 15, invented a tool for breast cancer detection. She was one of 10 women honored at the event.

“Wow! Women of Worth. Celebrating tonight with the incredible Brittany Wenger. Google her! At 15 years old she started a program that has helped detect cancer with 99% accuracy. She’s 19 years old now and has only just begun to change our world. I’m humbled to have been her date. Who inspires you? #bethechangeyouwanttosee #lorealwomenofworth,” Lively wrote on Instagram.