"My expected due date is March 6th," she told the publication, adding that she's currently "14 weeks" pregnant.
She admitted that she was nervous when she first learned she was expecting. "At first it was scary and emotional and it just takes you by surprise. I found out at five weeks, so I've known for a long time. Once it sunk in, we started getting more and more excited," she said.
Lowell, 26, said that no one knew about the pregnancy except for family, friends and Teen Mom OG cast and crew. "[Cast members] Maci [Bookout] and Amber [Portwood] also knew," she said. "When I told them, they were both super excited for us."
She added that her mom was a calming force.
"When I first texted my mom, I sent her a picture of a pregnancy test and I wrote her like, 'What the hell am I gonna do?' My mom was like, 'Are you kidding? It's going to be amazing.' She was super excited," Lowell added.
She said her dad is hoping for a girl and said he was "jumping off the walls."
"He wants another granddaughter! Everybody was just super supportive," she added. "Tyler's mom was also really excited."
Baltierra shared a link to a story about the baby's due date on Twitter Monday alongside a photo of Lowell showing off her baby bump.
"DUE DATE REVEALED!" Baltierra wrote alongside a heart-eyed emoji and a smiling emoji.
The couple previously told Us Weekly that they're both hoping for a baby boy.
"I think we both want a boy for sure, but also we have Nova," Lowell said, referring to her and Baltierra's 3-year-old daughter. "So it's, like, if we're just meant to have girls, we're meant to have girls."
The couple, who wed in 2015, placed their eldest daughter, Carly, now 9, for adoption in 2009.
Lowell added, "With Carly too, it's like Tyler just makes girls. The guys make the gender."
Baby no. 3 is especially significant for Lowell and Baltierra because they recently suffered a miscarriage, which was documented on the MTV series. The couple has been referring to their baby due in March as their rainbow baby, which is a child born after miscarriage, stillbirth, neonatal loss or infant or child loss.
"It was a huge shock at first," she told Us Weekly. "We were not planning it, especially after the miscarriage and how I went downhill with my mental illness."
THIS. RIGHT. HERE....NAILED IT!!! 🙌🏻💯👏🏻🙏🏻 //t.co/8p8H38BOSC— Tyler Baltierra (@TylerBaltierra) September 14, 2018
The 26-year-old dad retweeted someone who wrote, "If no one with depression had kids the world would start shrinking at an alarming rate. If you are one of the lucky few never to experience it. Give a prayer of thanks and don't talk about what you do not understand."0comments
"THIS. RIGHT. HERE....NAILED IT!!!" Baltierra wrote when he shared the tweet.
Teen Mom OG returns for its eighth season premiere Monday, Oct. 1 at 9 p.m. ET on MTV.