”Kim Kardashian isn't due to give birth for several months, but when she does, she'll be looking to sister Kourtney for more than just parenting tips.The pregnant reality starlet, who is expecting her first child with boyfriend Kanye West, took to her blog on Jan. 3 to marvel at Kourtney's incredible post-baby body on the cover of Us Weekly.Kourtney, for her part, told Us Weekly's West Coast Bureau Chief Rebecca Bienstock that she couldn't have done it without her younger sis. "If she wasn't scheduling the workouts, I probably wouldn't have been as motivated," she said. "If one of us isn't in the mood, we push each other."Now a lean 106 pounds, the mom-of-two -- to Penelope, 6 months, and Mason, 3, with partner Scott Disick -- works out regularly with celeb trainer Tracy Anderson, who is also helping Kourtney's 12-weeks-pregnant sister stay fit."Tracy Anderson is keeping me in shape!" the first-time mom-to-be wrote on Jan. 3. "She is helping me make the adjustments necessary to keep me feeling happy, healthy and most importantly create a workout plan that is safe for the baby. It's really important for me to have a fitness routine that works for my body and my schedule and I'm really happy with the workout plan Tracy is working with me on."Us Weekly