(NEW YORK) -- More often, cases of the opposite sort make headlines: a woman who doesn't know she's pregnant gives birth. Earlier this month, a 44-year-old Michigan woman arrived at a hospital thinking she had a hernia then delivered a 10-pound-baby later that day.
But doctors also report cases of women who believe they're in late-term pregnancy but aren't.
In classic instances of the rare condition, known as pseudocyesis, these women even have pregnancy symptoms, everything from an elevated presence of pregnancy hormones to enlarged breasts.
"The only ones (not present are) heart tones of the baby, an actual picture of the baby, and delivery," said Dr. Paul Paulman, professor of family medicine at the University of Nebraska College of Medicine. "Everything else has been shown."
But the fact that a woman's beliefs alone could make her body act as if it's pregnant, according to Paulman, makes some sense because the pituitary gland, a pea-sized structure at the base of the brain, helps control menstrual cycles and milk secretion.
"The brain decides to be pregnant," he said. "The good news is as far as physical harm, unless you're having a c-section you probably won't get hurt," Paulman said.
Doctors sometimes do get fooled. Two years ago an emergency c-section was performed on a woman who wasn't pregnant after doctors tried to induce her for two days at a North Carolina hospital. Two physicians were disciplined.
There aren't any reliable statistics that could help explain how commonly women get pseudocyesis, according to Dr. Orit Avni-Barron, a psychiatrist and director of The Fish Center for Women's Health at Brigham and Women's Hospital. Typically the condition occurs in women ages 20 to 39 and it has been observed in women of all races and income levels in this country, said Avni-Barron, who published a report on pseudocyesis in 2010. Research that does exist is based only on case studies -- no randomized trials, Avni-Barron said.
Dr. Paulman agrees. "It's really impossible to track," he said. "The people really don't want to hang around and answer a bunch of questions after they find out they're not pregnant."
Gecsi said women often get embarrassed after finding out the truth. Typically they accept the fact and go home to "normal lives," she said.
Pseudocyesis isn't a recent phenomenon or even one limited to humans. The illness 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. Today, shows including Glee and Law and Order have featured characters suffering with false pregnancies.
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.
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.
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