"When I first found out, I was a little scared," the 27-year-old Teen Mom OG star told Us Weekly. "I just kind of sat down and thought about it and realized that it was a big step in my life and it was a good thing actually, and I was really happy within 30 minutes."
After the first shock of hearing the news, she told Glennon and "it was nothing but happy thoughts," adding that the two are "both very happy."
Portwood confirmed the happy news after a report from PEOPLE earlier this week. A source told the magazine she told her family first.
The new baby is Portwood's first with Glennon, who is a cinematographer. The two reportedly met during filming of Marriage Boot Camp, where Portwood was paired with ex-fiance Matt Baier.
In August, Shirley told Us Weekly he didn't really know Glennon, but thought Portwood was rushing into another relationship after breaking up with Baier.
"So far it's good I think," he told Us. "I think she should have waited a little bit and really felt it out, but that's OK."
Portwood previously said on Teen Mom OG in May that she didn't want to have any more children. She was re-diagnosed with borderline personality disorder and bipolar disorder and will have to take medications for the rest of her life.
"I just got re-diagnosed for Borderline Personality and Bipolar Disorder, and I've been taking three medications now that I need to take for the rest of my life," she said in the episode. "I can't, I can't get pregnant on this medication."