Lowell's mother, April Stotts, confirmed the news to Us Weekly on Tuesday.
"[Catelynn] was crying when she knew for sure and so I was like, 'Are you happy? Are you upset?' And she was like I'm happy!,'" Stotts said of her daughter's pregnancy.
MTV documented Lowell's pregnancy and adoption process on the very first season of its hit, 16 and Pregnant. Lowell and Baltierra later appeared on Teen Mom.
Just last month, the couple said they were trying for another baby.
"I am an adult and I can tell when I'm ready and idc what ANYONE says I'm gonna do me! We ARE READY for a baby," Lowell tweeted.