During Vegas shooting, pregnant Brittany Aldean feared she'd never hold her child

Brittany Aldean wrote she feared she would never get to hold her unborn baby.

Brittany Aldean, who is expecting the couple's first child later this year, was in a tent behind the stage at the Route 91 Harvest Music Festival when the shooting started Sunday night. A gunman opened fire from the 32nd floor of the Mandalay Bay Resort and Casino, killing 58 people and injuring almost 500 others. The 29-year-old former cheerleader, who first wrote about the attack in an Instagram post early Monday morning, went into more detail in a post on the same platform on Wednesday.

"It’s been hard to process what happened the other night ... Still feel like I’m in a daze," Brittany Aldean wrote. "First and foremost, thank you to the first responders. It amazed me at the time and still continues to -- these people completely put everyone else’s lives before theirs and we are all forever grateful."

She then detailed where she was when gunman Stephen Paddock opened fire on the crowd of 22,000 people from his hotel room in what authorities are calling the deadliest mass shooting in modern U.S. history.

"When the gunfire started, I was not with Jason, but with some friends in a tent closer to Mandalay," she explained. "As you can imagine, my first instinct was to run to him and his was the same."

In a video of the shooting, Jason Aldean can be seen leaving the stage after gunfire erupted.

Brittany Aldean revealed what was going through her mind as she ducked for cover.

"As we laid behind equipment onstage with some of our road family, bullets flying past... all I could think was, ‘I never even got to hold my baby,’” she wrote. "We all made sure the others knew we loved them and then ran for cover where we stayed for the next couple hours. (Not knowing if there were multiple shooters, where the bullets were coming from... NOTHING)."

She then acknowledged, "We were the lucky ones."

"I can’t put into words the pain and heartache we feel for the ones who are no longer with us," she added. "May God be with their families and friends during this horrendous time. Each and every one of you are and will forever be in our prayers."

Just after the shooting, Brittany Aldean posted that she and her husband were safe and that she was praying for everyone.

"Our angels were definitely watching over us tonight. No words for what happened... Just horrific. Praying for everyone," she wrote early Monday morning.

The Aldeans had just celebrated with a baby shower earlier in the weekend.

On Tuesday, Jason Aldean announced he was canceling his next three concerts, scheduled in California, "out of respect for the victims, their families, and our fans." He will return to the stage Oct. 12 at the BOK Center in Tulsa, Oklahoma.