After months of searching for answers about daughter Aliannah's developmental delays, Teen Mom 2's Leah and Corey Simms take her to undergo an MRI on Tuesday's all-new episode.
"Mommy would do it for you, but I can't," Leah, 18, says as she kisses her 13-month-old and sends her off into the procedure room to be sedated. "Be a big girl," adds Corey, 20. (Watch an exclusive preview clip above)
For the young parents, Ali's latest MRI will hopefully provide more details as to why she's developing more slowly than her twin, Aleeah.
Corey — whose wedding to Leah will be seen on an upcoming Teen Mom episode — says the little girl helped bring her parents back together following an emotional six-month split.
"I had feelings for Leah the whole time [we were separated], but whenever she came home from a doctor's appointment all upset, it hit me that Ali needs both of us together," he tells UsMagazine.com. "I knew that if we had Ali in a split-up home, that wouldn't help her at all. She'd have double the problems."
Though the tot's physical limitations, if any, have not fully been determined, Corey says their daughter is improving every day.
"She's scooting around on her butt now," Corey says. "If you put her up against a table or couch she will stand up by herself. She used to just sit there. She's really improved. Still, it's hard because we don't know if she's going to be limited in the activities she can do in her life. I told Leah that no matter what Ali has, no matter what is wrong, she'll live a very active life. As long as I'm able to get her out there, she'll be able to do it. Whatever she wants."
Teen Mom 2 airs Tuesday at 10 p.m. (EST) on MTV.
Sign up now for the Us Weekly newsletter to get breaking celebrity news, hot pics and more delivered straight to your inbox!