There are many medical mysteries that have plagued the minds of doctors over the years, though some are more weirdly fascinating than others.
A 30-year-old woman's 'phantom pregnancy' from 1990 is one of the more intriguing ones.
Paul Paulman, working in a family practice, was greeted by the woman, who on the surface had all the obvious symptoms of being pregnant. Even for the simplest of medical minds it was plain to see she was carrying a child.
She and her swollen belly stumped doctors though, as after an ultrasound it was shown that she had no uterus. It wasn't a discovery for the lady in question - she was fully aware that she'd had a hysterectomy, making pregnancy for her impossible - but there seemed no other explanation.
The term for this sort of thing is pseudocyesis, a rarity in the medical world, with only 80 cases showing up between 2000 and 2014.
Because it's so rare, and because it does genuinely look like the sufferer is pregnant, it's not really questioned by doctors and nurses. In fact history shows that on a few occasions, after trying to induce labour and failing, C-sections have been performed, only for there to be no baby present.
The symptoms, classified as a somatoform disorder by the Diagnostic and Statistical Manual of Mental Disorders (DSM-5), are far more common in other mammals, believed to be caused by changes in the endocrine system of the body, when hormones cause physical changes.
There's also evidence to suggest that it could be psychological when the symptoms of gestation take over, almost like mental health disorders like anxiety, when certain symptoms mimic that of heart attacks or strokes.
In terms of research, pseudocyesis is a condition that's largely unknown due to the lack of cases. With regards to the theory that psychology is the route of the issue, Paulman says that false pregnancies are more common in developing countries where an integral part of a woman's role in society is to be a mother, Tonic reports.
As social pressure or a woman's desire to have a child builds up, eventually so do the symptoms of pseudocyesis.
In all cases there will be abdominal distension, usually seen as a child develops in the womb, with natural signs such as amenorrhoea, morning sickness and tender breasts all potentially being present.
The condition is also possible in men, though is obviously even less common, and is believed to be a part of couvade syndrome, also known as sympathetic pregnancy. This is a completely psychological condition occurring in men who watch their partner struggle through the tiresome process.
But with the disorder being so uncommon, preventing opportunities for full research, it seems likely to remain a mystery for years to come.
Featured Image Credit: PA