Kardashian, a member of the U.S. TV reality show family famous for being famous, has since given birth to a daughter with the unusual name of North West, West being the surname of the child's father, rapper Kanye West.
Kate's royal baby is due any day now, and while she and Prince William travel in different social circles and have a regal heritage far removed from the Kardashians, the public interest and attention focused on both couples has been intense.
While some people may question the relevance of real people paying any serious attention to the latest news of Kate, Kim or any other celebrity parent, psychologists say such interest is understandable and natural.
"The human being is hardwired to worship something, and traditionally that's been a religious figure," says Jim Houran, a New York-based psychologist and expert in celebrity culture.
"But now, more and more people are turning away from organized religion and it's being replaced with something and to me that's these more secularized saints and gods that we call celebrities."
In the case of Kate and William, there's an extra factor at play: royalty.
"Regardless of the celebrity, we tend to see them as these people on pedestals," says Houran. "When you add on top of that a real aura of regality, that just sort of sweetens the pot."
Glimpses into private life
Anything of a personal nature that a celebrity does also seems to take on extra resonance.
"I think whenever celebrities do anything that gives us a glimpse into their private life, fans will latch on to that," says Houran, adding "you don’t get much more personal than newborns.
"So whenever celebrities add onto their families we'll naturally be captivated by that just like whenever celebrities do something wrong, we get captivated by that as well."
Daniel Kruger, an evolutionary psychologist and research professor at the University of Michigan in Ann Arbor, says these high-profile births have become such a media phenomenon because they combine two fascinations humans have as part of our evolved heritage: an interest in infants and children, and an interest in high-status individuals.
That interest in small children is very much a characteristic of our species and any species where an adult other than a mother may provide parental care to newborns or younger offspring, says Kruger.
"You see this happening in other primates," he adds, noting documentaries have been produced focusing on chimpanzees giving birth at zoos, and the offspring being introduced to other chimps. "You just see the fascination in their faces with the new infant."
That other human fascination, with high-status individuals, might even have a practical payoff for those of a lower social position, Kruger says.
"It provides benefits for others because they're better able to create alliances and advance their own social position by knowing what's going on at the top," he suggests.
"So you combine these two things and when you have high-status individuals having babies, that’s going to draw a particular amount of attention."
Houran thinks the pending royal birth has triggered interest particularly because it is a "happy event."
"Celebrities do a lot of good," he says, because beyond providing entertainment, they also offer a form of escapism.
"I think that this is actually a particularly well-timed birth amidst a lot of turmoil in the world, so it gives people something positive and happy to think about and to pay attention to above and beyond the normal turmoils we tend to see on the TV."
But there is a limit to how much celebrity attention is a good thing.
"There does seem to be a fine line between functional and dysfunctional interest in celebrities," says Houran.
"And I'd say that probably the best litmus test for that is to what degree is your interest voluntary or not."
Talking about Kate or Kim around the watercooler or over dinner with your best friend is fine — once you have done that, you can go back to your real-world activities. Spending a lot of time trying to meet a celebrity or insert yourself into his or her life, especially at the expense of your normal relationships, is not such a good thing.
That there is interest in a pending royal or celebrity birth is nothing new.
Carolyn Harris, a Toronto-based royal historian, goes back to the 1500s and the birth of the child who became Queen Elizabeth I as a prime example of a high-profile pregnancy that attracted a lot of anticipation.
"Henry the Eighth had created the Church of England, arranged for his own divorce from his first wife, Catherine of Aragon and had remarried Anne Boleyn," she says. The anticipation was that she might delive a long-awaited male heir.
At that time, in a way that now seems quaint, word spread through diplomatic correspondence, or city dwellers wrote to friends and relations in the country.
"If you look at the diplomatic correspondence from Tudor and Stuart times, the fact that Anne Boleyn mentioned at court that she had a great craving for apples was seen as her way of announcing that she was expecting," in this case expecting what turned out to be the future Elizabeth I.
Throughout the 20th century, high-profile births and celebrity youngsters captured the popular imagination of their era for a wide range of reasons, whether it was the kidnapping and murder of toddler Charles A. Lindbergh Jr. in 1932, the birth of John F. Kennedy Jr. in 1960, or a celebrity of a different form — the first test-tube baby, Louise Brown, in England in 1978.
More recently, other celebrity births have been the stuff of tabloid headlines, whether it was the first "Brangelina" baby in 2006, Shiloh-Jolie Pitt, the daughter of Hollywood A-listers Brad Pitt and Angelina Jolie; or Suri Cruise, daughter of actors Tom Cruise and Katie Holmes.
And we can expect more of the same as celebrity worship isn't going to go away.
"We are in a media- and entertainment-saturated society so you can't get away from it. It's just part of our culture now," Houran says.
If it's entertainment you turn off, that's fine, Houran says. "If it’s like an addiction, that's a problem."