Pseudocyesis isn't a recent phenomenon or even one limited to humans. The illness, classified as "somatoform disorder" in the Diagnostic and Statistical Manual of Mental Disorders, a reference manual published by the American Psychiatric Association, has been observed in other mammals such as dogs. Even medieval writings refer to the condition.
Many historians argue that the English queen Mary Tudor, known as "Bloody Mary," suffered from pseudocyesis and ordered repeated burnings at the stake in part out of stress from an inability to produce an heir. Today, shows including "Glee" and "Law and Order" have featured characters suffering from what appears to be pseudocyesis.
Pseudocyesis is most common in developing nations where large families are valued and a woman's identity is tightly wrapped up with being a mother, Avni-Barron said.
"It's almost a social disorder," she said. "It's fascinating."
The condition appears to be rarer today in the developed world as family sizes have shrunk and a woman's primary role is no longer only to raise children, she said.
"Having kids is not such an important factor (here) as in other cultures," Avni-Barron said. However, "immigrants can be more at risk," she said.
Risk factors include a strong desire to have a baby, low self-esteem, and a tendency to misinterpret things and come to conclusions easily, she said. If depression is present, it can affect neurotransmitters such as serotonin which interact with reproductive hormones to "cause a real change" in a woman's body, Avni-Barron said.
Doctors who encounter such women should clearly explain to them the facts of the situation, said Paulman, who once encountered a woman who had undergone a hysterectomy but still believed she was pregnant. He had to show her an ultrasound and tell her, "the equipment isn't there," he said.
But sometimes even showing an image of a vacant uterus isn't enough to shake the beliefs of a woman -- or her body's mechanisms.
One New York City area woman told her doctor that her baby wasn't visible in the ultrasound because it was hiding under her ribs, a friend of the woman, who asked to be quoted using only her middle name, told ABCNews.com.
The woman's insistence about her condition is alienating everyone around her, her friend said.
"It's just a big, big burden on my heart and my friends," Joy said. "We don't know what to do. This is a young person (and) it's going to destroy her life."
Her friend who she says suffered from the condition -- a former personal trainer in her mid-20s who is thin and always has been -- has a history of lying and exaggerating details of her life, Joy said. After repeated pregnancy tales in recent years her friends thought her latest pregnancy claim was just another ruse. Now, making matters worse, she really looks pregnant, Joy said.
"She sent a video to a friend recently to try to prove (her) pregnancy," Joy said. "There's a belly, there's no mistaking it. She looks like she's showing six months, it's disturbing. She picked up her shirt in the video and did a 360 of it."