During Thursday's episode of "The Kardashians," the Poosh founder shared the worries she had regarding her postpartum body ... and it had nothing to do with the baby weight she gained.

While Kourtney admitted she'd like to drop 10 pounds after welcoming baby Rocky, she said she was more worried about keeping her "vagina intact" -- watch the clip, which is why she said she's avoiding any vigorous activities, like jumping or running.

Namely, Kourtney was concerned about having a vaginal prolapse ... which she thought meant her vag would "fall out." The reality star wasn't entirely accurate with her definition, as prolapse is more when a vagina slips out of position ... though that sounds equally uncomfortable.

This explains why Kourtney -- who is also a mom to kids Mason, Penelope, and Reign -- was doing what she could to prevent the condition from happening ... including Pilates and walking.

Kourtney's admission comes a week after the mother of 4 revealed she and her husband Travis Barker got busy to induce labor ... when she was already 3 centimeters dilated!!!

The couple was so eager to have little Rocky on Halloween, they tried everything in the birthing playbook to make it happen. As TMZ previously reported ... Kourtney did end up going into labor on October 31 ... but Rocky arrived in the world in the early hours of November 1.