Kim Kardashian posted this photo on Instagram of Khloe Kardashian, Kylie Jenner, Kendall Jenner, Kris Jenner, Kourtney Kardashian, Rob Kardashian, and herself going bowling to celebrate Kourtney's birthday. Credit: Courtesy of Kim Kardashian

This is how the Kardashians bowl! The reality show family kicked off Kourtney's birthday celebrations this week by enjoying a casual bowling night in L.A. on Wednesday, April 17.

The birthday girl, who turns 34 on Thursday, posed with mom Kris Jenner, sisters Kim, Khloe, Kendall and Kylie, and brother Rob in one group photo shared on Kim's Instagram. The whole family dressed in their best bowling attire, with pregnant Kim showing off her baby bump in a pair of ripped jeans, a black shirt and blazer and black heels.

Kourtney's boyfriend Scott Disick and children Mason, 3, and Penelope, 8 months, appeared to be missing from the group, but several of her girlfriends were there to celebrate her special day. "Original DASH dolls hit the lanes," Kourtney captioned one cute shot. "Better than when we were hitting the clubs. Love you guys!"

The mother of two goofed around with her gal pals by taking photos of them doing "splits and high kicks" in front of their lane. She also bowled with a SpongeBob SquarePants ball.

First-time mom-to-be Kim wrote a special message to Kourtney on Twitter Thursday. "Happy birthday to my big sister and mentor," she tweeted with photos of them together. "I love you so much."