Cases of a rare birth defect in which a baby's bowels are outside the body have doubled this year in Wales.
A scan revealed Stacey Harding's baby has the condition
BBC One Wales' Week in Week Out programme has revealed that the condition is more common in Wales than anywhere else in the world.
Tuesday's programme features a 15-year-old whose baby will be born with the complaint, called gastroschisis.
The causes of the condition are still unknown.
Teenager Stacey Harding, from Kenfig Hill, near Bridgend, is not making too many plans.
She is one of 30 mothers-to-be whose ante-natal scans have revealed the condition.
As soon as it is born, her baby will have to undergo an operation which has a 90 - 95% chance of success.
"We're not buying anything until she's well out of hospital, so we know that everything is OK," she said.
Stacey is supported by her mother Linda, who says the baby's condition is a constant concern.
"You do still worry, because you know there is that chance that it's not going to go in your favour," she explained.
Surgeon Simon Huddart says he is deeply concerned
One baby in every 1,000 born in Wales this year has gastroschisis, but the reason for such a high proportion here is still baffling the experts.
In a typical year, an average of 16 babies would be expected to be born with the condition in Wales.
Paediatric surgeon Simon Huddart from the University of Wales Hospital, Cardiff, has operated on many of the babies.
"The alarm bells are ringing, partly because of the number, and partly because of the distribution of the cases throughout Wales," he said.
Mr Huddart belongs to a panel of experts set up to investigate the unexplained increase. He said he felt much more research was needed to establish the reasons.
He told the programme: "When there is a doubling of cases such as this, I think there is a need for research resources to go into seeing whether there is an obvious cause - and whether there is any reason to suppose the increase is going to keep on going."
Week In Week Out is screened on BBC 1 Wales at 2235 BST on Tuesday.