Early in the episode, as Arizona is walking away from Alex, the camera pans wide and Arizona is seen to have two fully functioning legs with no evidence of a prosthetic.
When Drs. Robbins & Kepner first treated Jenny in Episode 17, it was said several times that she was "6 months pregnant" (which would be approx. 24 weeks along). In this episode, which is presumably several weeks later, Jenny experiences complications and it is said that it's too early to deliver because the baby is "barely viable outside that womb" because she is only 24 weeks along.
About 5 to 6 minutes into the episode, after checking the pregnant woman for the first time, Arizona walks away from Karev and you see two bare and fully functional legs and feet.. a bit odd, after the amputation a couple of years ago.