An Italian woman is due to give birth in a hospital in Rome this week to a baby girl - before returning three months later to have triplets.

If both deliveries are successful, it is thought that this will be the first such case in history.

I remember asking the doctor to make sure because I just couldn't understand how it was possible

She told Italian television: "When I was at the sixth month of my pregnancy and went to see the doctor for the usual tests and scans, he noticed that, apart from Denise, there were another three babies.

"I didn't believe it at first. I remember asking the doctor to make sure because I just couldn't understand how it was possible.

"The difficult thing is not knowing what is going to happen after Denise is born. After that it is all suppositions and theories."

Not possible

Professor Ian Craft, director of the London fertility clinic, said it should not be theoretically possible for a woman to be pregnant twice at the same time.

He said: "Normally when you are pregnant you switch off your ovulation, and you don't then ovulate again and you have no periods until your child is born and you are at least part the way through breastfeeding.

"I have never seen it in my whole professional career."

Professor Craft said the condition, known technically as superfecundation, does occur rarely in animals.

However, he said it was extraordinary for someone to conceive naturally and then to spontaneously ovulate three eggs again. The chance of having triplets is only one in 6,000.

"How often would you expect these two combinations to go together? You are more likely to win the lottery."

Professor Craft said there was a high risk that the triplets would be born prematurely.

He said there were also difficult questions about how the first child should be delivered to minimise risk to the triplets.