Khloé Kardashian had a hard time connecting with her son after the 'transactional' nature of surrogacy. A counselor explains how stress affects bonding.

• Khloé Kardashian's son, Tatum, was born in August via surrogate.
• Kardashian said she's less connected to Tatum than her daughter, True, whom she delivered.

On Thursday's season-three premiere of "The Kardashians," Khloé Kardashian said she'd had a difficult time bonding with her son, Tatum, after welcoming him via surrogate in the summer. The whole experience messed with her mind, she said, calling surrogacy "really the weirdest thing."

She went on to tell her sister Kim and family friend Scott Disick about the experience: "It's really hard for me."

While Kardashian knew that she would be welcoming a son, she said the reality of having a baby didn't kick in until her surrogate was in labor.

"I definitely buried my head in the sand during that pregnancy," she said. "So when I went to the hospital, I think that was the first time that it really registered."

She added: "I definitely was in a state of shock, I think, from my entire experience."

Kardashian hasn't said why she used a surrogate. But last year, someone told People that she struggled to get pregnant after having her daughter, True, who is 5. In addition, during the surrogate's pregnancy, Kardashian found out that her children's father, Tristan Thompson, got another woman pregnant.

"It has nothing to do with the baby," Kardashian said of her trouble bonding.

There may be a physical reason for Kardashian's trouble bonding

During childbirth, the body releases the chemical oxytocin, which helps people bond, Cheryl Groskopf, a licensed marriage and family therapist and professional clinical counselor, said. Parents who don't birth their babies don't have that biological aid in bonding, she told Insider.

At the same time, the decision to use a surrogate is often stressful, she said, which can also complicate bonding.

"The stress around having a child via surrogacy can be overwhelming, which often impacts emotional and physical intimacy," Groskopf said.

Having many conflicting emotions seemed to play into Kardashian's difficulties.

"I felt really guilty that this woman just had my baby. Then I take the baby and go to another room, and you're separated," Kardashian said. "I felt it was such a transactional experience because it's not about him."

Khloé and her sister Kim had different experiences with surrogacy

Kardashian discussed her challenges bonding with her sister Kim, who delivered two children and had two more via surrogate.

"Kim said hers was easy," Khloé said in the episode. "This is not easy."

Unlike Khloé, Kim hasn't mentioned having any trouble bonding with her kids born by surrogate, but she acknowledged that experiencing the difference between those two paths to motherhood could be complicated.

"I do think there is a difference when your baby is in your belly. The baby actually feels your real heart. It touches your organs," Kim said. "Think about it. There's no one else on this planet that will feel you from the inside like that, your heart."

Kim added that Khloé's stress about the surrogacy might have contributed to how she's feeling now.

"She had a hard time accepting the whole process," Kim said.

Despite her difficulties, Khloé is determined to share her challenges with surrogacy.

"I wish someone was honest about surrogacy and the difference of it," she said. "It's still great. It's just very different."