The earlier a baby is born, the higher the risk of poor health, research suggests
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).
Worry: Research has found that the earlier a baby is born, the greater chance of health issues throughout its life (Stock image)
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 per cent more likely to suffer a long-standing illness than those born at 39 to 41 weeks, and were around 10 per cent more likely to suffer asthma or wheezing.
Aged five, children born at 37 to 38 weeks were 40 per cent 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.
Be careful: Pregnant women are being urged to lead a healthy lifestyle to improve the chances of a healthy baby
'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.
'However, this small group of babies (approximately 8,000 births annually in England) is far outnumbered by more mature preterm babies, born at 32 to 36 weeks,' the team said.
'This group has been understudied until recently, and babies of this gestation, although immature, have been considered to be at minimally greater risk of adverse outcomes than babies born at 37 weeks or later.
'Even less well understood are the risks associated with birth at 37 to 38 weeks (125,000 births annually), as this has been thought to represent term gestation.
'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.'
Leanne Metcalf, assistant director of research at Asthma UK, said: 'This is not the first piece of research to indicate that every week spent in the womb is important for a baby in order to reduce its risk of developing asthma in childhood.
'The advantage of this study, however, is its scale in terms of the number of children whose asthma development compared to their gestational age has been measured, and the fact that it has looked at babies who are born just a few weeks prematurely.'
She said it was reasonable to believe the gradual development of the lungs might influence the risk of asthma.
'There are a number of things that pregnant women can do to reduce the risk of prematurity in their baby, including maintaining a healthy weight, staying active and avoiding stress, smoking and infections.
'Obesity, stress and smoking have also all been separately linked to an increased risk of asthma in children, smoking especially, so taking steps to avoid them will enable pregnant women to give their baby the best possible chance of a healthy childhood.'