Shanann Watts had been looking forward to a party on Saturday to disclose the gender of her third child, CNN affiliate KDVR said, quoting a friend.
But the Colorado woman and her two daughters Bella, 4, and Celeste, 3, were found dead on Wednesday. Her husband, Chris Watts, was taken into custody.
Today, the community is in shock and mourning the losses.
Shanann Watts' friend Ashley Bell told KDVR the "gender reveal" party was slated to be held at the Watts' home.
"They were always so happy. They were always so — I'm completely lost for words," Bell said.
Shanann Watts was 15 weeks pregnant. She posted a video of her announcing the pregnancy to her husband.
A candelight vigil is to be held in the Wyndham Hill neighborhood on Friday night. A makeshift memorial with flowers and stuffed animals is growing outside the Watts' house.
Tim Sunderland, community manager for the Wyndham Hill Master Association, the homeowner association, said the clubhouse will be open at 5 p.m. local time for people to congregate and comfort each other.
"Very surprised. Very shocked," said Sunderland, who described the area north of Denver as peaceful and quiet. "It's a very good community."
Watts faces three counts of first-degree murder and three counts of tampering with a human body, police said. He is being held without bond, with his next court appearance scheduled for Tuesday.