The women who are convinced they're pregnant, but aren't carrying a baby.

Earlier this month, Katie Horneshaw wrote a piece about the unspoken trauma of infertility.

She described on news.com.au her desperation and how tightly she clung to hope. Having a baby had been her only non-negotiable. For Horneshaw, a child of her own would be the thing – perhaps the only thing – that could “grant me my happiness’.

But as I read, there was a particular passage that gripped me. She wrote:

“Every month, I would beg myself not to let my hopes soar too high. Yet every month, the phantom symptoms would come. The niggling in my breasts, the nausea after eating. The images of telling mum; of her crying softly on the other end of the phone; would creep across my mind until finally I would let down my guard and surrender to excitement.”

But of course, every month she was greeted with a dreaded stain in her underwear, which she says “…struck with pain like lightening”.

The term "phantom symptoms" piqued my interest. I had heard of phantom limb and even phantom eye syndrome, which are relatively common conditions where people feel sensations in parts of their body that they no longer have. But phantom pregnancy? Now that sounded interesting.

To be clear, what Horneshaw experienced was very normal for a woman struggling with infertility. But for some women, the sensation of pregnancy can last for nine months. In fact, for some it can last even longer.

Phantom pregnancy or false pregnancy, officially referred to as pseudocyesis, refers to the appearance of "clinical signs and symptoms associated with pregnancy" when the individual is not actually pregnant.

The condition presents itself in women as well as men, and has even been observed in animals. It is well documented throughout history, with Elizabethan's believing that phantom pregnancies "were the work of demons".

Our understanding of the illness has (thankfully) come a long way. It can develop as a result of changes in the endocrine system, which releases hormones very similar to those secreted during pregnancy.

We also know that hormones are very much influenced by our own psychology. Thus, by wishing it so, some women can almost "bring on" the signs of pregnancy. It has been known to occur in women who have experienced trauma, such as the death of a spouse or multiple miscarriages.

US obstetrician Dr Norman Duerbeck says on BabyCenter.com that some women even 'see' a foetus on the ultrasound screen. Once they are informed that they are not pregnant, he says "it's very difficult for patients to accept".

Symptoms include rapid stomach growth, tender breasts, morning sickness and the absence of a period. Some experience the sensation of a baby moving in their stomach, known as "quickening". One per cent of women will even experience false labour.

In 2013, a 37-year-old woman in Brazil underwent an emergency c-section, after arriving at hospital with a large stomach, 'labour' pains and proof of pre-natal treatment.

It was discovered during surgery, that she was not, nor had she ever been, carrying a baby.

The case was officially registered as a phantom pregnancy. This is distinct from consciously feigning pregnancy, which is termed a 'simulated pregnancy'.

 Although increasingly rare, there are still cases such as these all over the world.

Apart from being fascinating to explore, the condition powerfully demonstrates the inextricable tie between the mind and the body.