On scrubs why did Kim lie to J.D. about having a miscarriage?

In Scubs; Season 6, Episode 8, J.D. took Carla, Elliot, Janitor, Keith and Ted along for the ride to Tacoma for Kim's first ultrasound just to find out from Kim that she had a miscarriage, but later on in the show as it turns out, Kim is still pregnant with his child. Why did she lie to him?