What's A Hysterical Pregnancy?

Late in last season's hit sitcom 30 Rock, the character Jenna experienced a "hysterical pregnancy" during a gas leak, where she had all the signs of being pregnant without actually being pregnant.  I couldn't help but wonder... is that really a thing? 

Not only is it a thing, but women and men can experience it!

According to WebMD: 

False pregnancy, or pseudocyesis, is the belief that you are expecting a baby when you are not really carrying a child. People with pseudocyesis have many or all of the common symptoms of pregnancy [swollen belly, stopped menstruation, feelings of fetal movement, nausea/vomiting, milk production, etc] with the exception of an actual fetus.  

This condition is very rare, occurring in only 1 to 6 out of every 22,000 births.  It is most common in women aged 20 to 44, although it can affect women of all ages. 

In rare cases, even men can have a false pregnancy. Some men experience a related phenomenon known as couvade, or sympathetic pregnancy. They will develop many of the same symptoms as their pregnant partners -- including weight gain, nausea, and backache.

People suffering from a false pregnancy can sometimes even test positive on pregnancy tests!

What can cause hysterical (false) pregnancy?

According to an article in the NY Times:

Though scientists are still largely baffled about what causes it in humans, recent case studies and studies of similar conditions in animals are beginning to provide insight, exploring the role of hormones and psychology.  

Psychiatrists have suggested that pseudocyesis occurs in patients who desperately want to become pregnant — or who have a strong desire to be involved in a family member’s pregnancy experience.   

In a recent issue of the journal Psychosomatics, Dr. Biju Basil, a psychiatrist at Drexel University, reported a case of a woman who went through false delivery at the same time her son’s girlfriend was giving birth. "She started having labor pains..." Dr. Basil speculated that “she wanted to [subconsciously] play a more active part in this new life that was coming into the world.”  

Still, for all the theories about false pregnancy’s origins in the subconscious, biological studies suggest it may be in part hormonally mediated as well... Case studies at the University of Michigan and elsewhere indicate that many patients have elevated levels of hormones like estrogen and prolactin — compounds that can cause physical symptoms like abdominal swelling and milk excretion...  

This raises the possibility that pseudocyesis is the result of a delicate mind-body feedback loop: an initial emotional state induces abnormal hormone secretion, which in turn has its own physical and psychological effects... anxiety may be one emotional state that helps set this feedback loop in motion.

Wow.  That's incredible. False pregnancy has written about since at least 300 BC!  The human body is a crazy thing.

And what's stranger -- dogs have much higher instances of false pregnancy than humans!