Catelynn recently documented a doctor's visit to get off of birth control with the hopes of expanding her brood -- and remarked afterward to producer Kerthy that the last time she removed her IUD, she conceived Nova quickly (within a month). And during tonight's Teen Mom OG episode, history repeated itself: Catelynn dressed their little girl in an "I'm Going To Be A Big Sister" shirt to tell an unsuspecting Tyler (remember, he wanted to be surprised with the news) about the upcoming addition.

And Tyler kept repeating the aforementioned sentence over and over again before asking his wife if she was lying. Cate insisted she wasn't being dishonest and brought out the positive pregnancy test results as proof.

"Oh my god!" Tyler stated as he looked at the sticks. "Fertile Myrtle!"

How will this life-changing news impact the family? Be sure to keep watching the Baltierra clan on Teen Mom OG every Monday at 9/8c.