Doctors are warning the trend towards more preterm deliveries could have considerable health implications.
Recent studies said the rate of preterm babies was increasing
Obstetrician Professor Andrew Shennan said early delivery can lead to physical and mental health problems, the British Medical Journal said.
A recent Denmark study said the preterm rate had risen by a fifth in 10 years.
Professor Shennan said doctors and parents should look to see if the number of preterm births can be cut.
The Danish research published by the BMJ in February found preterm deliveries had increased by 22% from 1995 to 2004.
It suggested fertility treatment, multiple pregnancies and elective deliveries were partly to blame for the trend.
But researchers also said factors such as smoking, teenage and middle-age pregnancy, obesity and social inequalities could also play a role.
Recent trends indicate the number of preterm babies are on the increase in England and Wales.
In 2004, 42,500 preterm deliveries were made, up by 2,500 from the year before.
Preterm deliveries account for fewer than 1 in 10 births, but result in three quarters of neonatal deaths and most neonatal intensive care admissions.
For instance, one in four survivors born less than 25 weeks' gestation have severe mental or physical disability. Even beyond 32 weeks, one in three children have educational and behavioural problems by the age of seven.
Professor Shennan, from King's College London, added: "Obstetricians should re-evaluate the risks and benefits of delivering babies earlier.
"If these findings from Denmark are true, the implications for neonatologists, health economists, teachers, parents, and children themselves are worrying.
"Other countries need to ensure that mechanisms are in place to detect such trends and assess their impact."
And he added if the burden on health was to be reduced, the number of preterm babies needed to reduced where possible, although he said identifying the underlying causes was difficult.
But a spokeswoman for premature baby charity Bliss said: "One of the main reasons we are seeing a rise in premature births is because of the improving medical care which means premature babies who would have died 20 years ago are now surviving and are going on to have a good quality of life.
"While this is good news, we need to make sure that the NHS is increasing the resources put into neonatal care to make sure we can cope with the ever increasing demand."