The couple previously hired a surrogate and, according to a source, the woman is now three months along in her pregnancy, Us Weekly reported.
Since it would be dangerous for 36-year-old Kim to carry the baby herself, the Keeping Up with the Kardashians star reportedly hired a mother in her late 20s located in San Diego, CA, to do it for her.
The pregnant woman whom Kim and the 40-year-old rapper hired has served as a surrogate before, Us reported, and even appeared with her family in a promotional video about the process.
The surrogate was referred by an agency and will likely welcome Kim and Kanye's child in January 2018.
The parents to North, 4, and Saint, 19 months, have reportedly agreed to pay $45,000 in 10 monthly installments of $4,500 for the surrogate, on top of the huge $68,850 deposit given to the agency, according to TMZ. In the case of twins or triplets, Kim and Kanye will pay $5,000 per additional child.
The surrogate's contract reportedly includes standard expectant-mom guidelines that prevent the woman from drinking, smoking, drug use, using hot tubs and saunas, eating raw fish and handling cat litter.
Reports surfaced in June 2017 that Kim and Kanye had hired a surrogate to carry their third child.
"Having more kids is definitely going to be a struggle," Kim admitted on the show before undergoing a procedure designed to repair her uterus and remove scar tissue.
"I've gone through so much with really bad deliveries that the doctors don't feel like it's safe for me to conceive again myself. This surgery is really the one last thing I can try. I want my kids to have siblings and I want to know that I did everything I could to make this happen."
However, a doctor told Kim at the time there were complications during the surgery and it didn't work out as planned. Kim was not only frustrated, but she told her friend Jonathan Cheban that she had a "full break down."
Kim later said in a confessional on her family's show: "Kanye and I are going to look into other options and see what we are comfortable with. I'm definitely leaning towards I want to try [surrogacy]... I always knew surrogacy was an option, now it's my reality. Whatever is meant to be will be."
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Kim underwent two surgeries after delivering North in order to conceive and carry her son Saint. She suffered from placenta accreta -- a condition that affects five percent of women giving birth in which the placenta stays attached to the inside of the uterus -- both times.