Babies born just a few weeks early have a higher risk of poor health, including asthma, than those born later, research suggests.
The earlier a baby is born, the worse the impact on their health, but risks are also evident for babies who are 37 to 38 weeks’ gestation - commonly seen as full term.
Data on more than 14,000 children born in the UK was analysed for the study, published online in the British Medical Journal (BMJ).
Researchers included data for moderate/late preterm babies (born at 32 to 36 weeks) and for those regarded as early term (37 to 38 weeks).
The earlier a baby was born, the more likely it was to suffer long-standing illnesses, asthma or wheeze and to be admitted to hospital in the first nine months of life for health issues, the most common being respiratory and gastrointestinal disorders.
But even those babies born at 37 to 38 weeks had poorer health than those born later, the study found.
For example, babies born at 37 to 38 weeks were 10% more likely to suffer a long-standing illness than those born at 39 to 41 weeks, and were around 10% more likely to suffer asthma or wheezing.
Aged five, children born at 37 to 38 weeks were 40% more likely to have been prescribed an asthma inhaler than those born at 39 to 41 weeks.
The researchers, including experts from the University of Leicester and the National Perinatal Epidemiology Unit at the University of Oxford, said: “Our results challenge widely held views that long-term health outcomes for moderate and late preterm babies (32 to 36 weeks) are similar to those for babies born at full term.
“The results also challenge perceptions about outcomes for babies born during part of the period of gestation that has traditionally been regarded as term (37 to 38 weeks).”
The experts found “increasing adverse effects with decreasing gestation” on a range of issues including growth, weight gain, long-standing illness, asthma or wheeze and hospital admissions.
Babies were assessed when they were aged nine months and again when they were aged three and five.
The experts said that research and resources were frequently directed towards very premature babies who have the highest risk of death and health problems.
“Our study casts doubt on these perceptions and highlights differences between these babies, now more appropriately classed as early term, and those born just one or two weeks later,” the team said.