Women can actually get pregnant while they are already expecting a baby

It might sound impossible, it turns out that women can actually get pregnant while they are already expecting a baby.

Called superfetation, while rare it does happen when a woman's egg is fertilised by sperm while another fertilised egg is already growing in the womb.

While doctors still don't know exactly why this happens, a spike in reproductive hormones is thought to be a key player.

There are a handful of documented cases of it happening in people and according to a French study in 2008 there were less than 10 documented cases worldwide.

It referred to a case study in which one foetus was noticeably smaller than a twin foetus in the same mum - which medics put down to one being conceived after the other.

In many of the documented cases, one twin is born significantly smaller than the other

A 1992 French study followed the case of a 32-year-old woman who was pregnant with two babies that had a four-week size difference.

When they were born, one was a month older than the other - leaving doctors baffled.

The woman experienced a normal 28-week cycle during her pregnancy and doctors believe her second baby was conceived after her second menstrual cycle once she had stopped taking contraception.

The twins grew at a normal rate for their age, but were born at the same time meaning the baby conceived second was born premature.

In another case in 2016 an Australian woman who thought she might never become pregnant gave birth to twins conceived ten days apart, reported the BBC.

Kate Hill was receiving hormone treatment for polycystic ovary syndrome, a condition that stopped her from ovulating.

She appeared to have conceived twins at different times despite only having unprotected sex once during that time.

The twin girls were born with different sizes, weights and gestational development, according to reports.

The mum’s obstetrician, Brad Armstrong, told the BBC the condition was so rare he was forced to search for it online.

“I could not find any literature in the medical review websites at all,” he s

Experts believe that women who are receiving hormone treatment to boost fertility during IVF are more susceptible to superfetation. This is because their ovaries are being stimulated in preparation for a baby as shown below image.

This is because their ovaries are being stimulated in preparation for a baby.

The French report noted that “the possibility of ovulation during ovarian stimulation in patients who are already pregnant has been observed during assisted reproductive technology” and that several peers had reported the “retrieval” of seven ovary cells in women receiving reproductive therapy.

It is these factors that could lead to superfetation occurring.