Grey's Anatomy costars Kate Walsh, Rebecca Gayheart and Sandra Oh were among the guests, who began arriving around 4 p.m., carrying gifts wrapped in pink and light pastel colors. Other guests brought gift baskets with baby blankets, clothing and stuffed toys.
Wearing a white summer dress, Pompeo, 39, arrived shortly after 4 p.m.
"She was glowing and had a big smile on her face as she walked in and her friends greeted her," a source tells Usmagazine.com.
The party was held on the back patio and tables were set up around Heigl's pool. To beat the heat, guests sat under umbrellas.
"There was a lot of laughter," a source tells Us. "It sounded like everyone was having a great time."