Babies born with a cleft palate are frequently being diagnosed so late that it jeopardises their normal development, surgeons have warned.
The Royal College of Surgeons says more than a quarter of babies with the birth defect have it missed at birth.
And 5% don't have the gap in the roof of their mouths detected until they are at least one month old.
Scott Deacon, a consultant orthodontist who runs the CRANE cleft palate database for the RCS, said the condition is serious and leaves babies at risk of failing to gain weight.
"We rely on the roof of our mouth to eat, talk and do many other things we take for granted," he said.
"It is crucial that a thorough visual examination of the mouth and palate is carried out within 24 hours of birth to ensure the baby receives the care and support they need."
Around 500 babies a year in the UK are born with a cleft in their palate alone, with no abnormality of their upper lip. But it takes just seconds to check a baby for the condition.
Rona Slator, clinical director of the West Midlands Cleft Service said: "A cleft has wide-ranging implications for a child's health and is certainly not just an aesthetic condition.
"All babies with a cleft will need surgical treatment once they are old enough. But prior to this the newborn and their family will require special bottles, guidance and help with feeding.
"Early diagnosis really is imperative."
Aaran Temple was not diagnosed until he was six years old and having speech problems.
As a baby, milk dribbled from his nose while he was feeding. But his mum, Mandy, was told not to worry.
She feels she was robbed of the chance to bond properly with him while he was young.
"All the things that I had been worrying about in the past and feeling guilty about - everything just fell into place," she said.
"He was like a typical cleft palate baby.
"I was really quite angry for a while, wondering why nobody had picked this up."