In the clip shared by E! News, Lowell is seen making cupcakes with Nova for a gender-reveal party when she shares the life-changing news.
"Mommy has a baby in her belly and tomorrow, the party is 'cause we're gonna find out if it's gonna be a little girl or a little boy," Lowell tells Nova, then asking, "Would you want a little brother or a little sister?"
Nova very sweetly replies that she would like "a little sister," but adds that she would love a little brother too.
Lowell teased on Instagram that she and her husband Tyler Baltierra had a big announcement to make before confirming to Us Weekly exclusively that they were expecting.
"The big news is that we are expecting our rainbow baby. This baby is our rainbow after the storm. I'm super excited," Lowell told the outlet. "It was a huge shock at first. We were not planning it, especially after the miscarriage and how I went downhill with my mental illness."
"We were going to wait a really long time. We were using protection and everything and still got pregnant," she added. "This baby just wanted to be here. It was very unexpected."
As Lowell mentioned in her statement, the couple suffered a miscarriage earlier in 2018, which took an understandably big toll on both of them.
"We just sat in the bed and cried and just held each other," Baltierra revealed in an episode of Teen Mom earlier this year. "I mean, there's nothing you can really do, so it felt very similar to Carly."
"I mean, Carly's a little different, because we have to—we get to see her every year, but it's a loss, and you feel it," he added. "Like, I feel like you process it as a loss. So I guess it's something I didn't really understand before."
Lowell previously suffered from mental health issues that may have been related to the tragic miscarriage. In Nov. 2017 she tweeted, "Well today I thought of every way to kill myself.. so I'm going to treatment."
She did indeed seek treatment and later opened up about why. "I decided I needed to get help from talking with Tyler and realizing that I maybe needed something more intense for myself," Lowell told MTV News. "For some reason, I just had a light bulb moment where I was like, 'Maybe I need extra help.' "
Lowell and Baltierra have announced that the due date for their new bundle of joy is March 6th.