Babies born as little two or three weeks before their 'due date' have a higher risk of health problems, such as asthma, according to new research.
The study conducted by researchers at Leicester, Liverpool, Oxford and Warwick Universities and the National Perinatal Epidemiology Unit, challenges the long-held belief that a baby is 'full term' from 37 weeks.
The researchers looked at health outcomes in 14,000 children born 10 years ago and found that babies born before 39 weeks have a slightly higher risk of health problems up to the age of five.
The findings, published in the British Medical Journal (BMJ), also suggested the earlier the baby arrived, the bigger the risk.
It was found that 17% of babies born a few weeks early had experienced asthma or wheezing as young children compared to 15% of those born full term.
However, the study authors stressed that the findings should not cause concern among parents as the results showed only a slight increase in risk.
Dr Elaine Boyle, from the University of Leicester, said: "We've found that it's no longer appropriate, as we have done previously, to think of babies as either being born at term or premature.
"What we've found is that there is a gradient of increasing health risk with increasing prematurity but this risk stretches right up until the time at which a baby should be born."
Experts believe the findings should be used to question the level of healthcare support and monitoring given to the families of children born before 39 weeks.
Andy Cole, chief executive of the special care baby charity Bliss, told the BBC: "This study highlights the need for the very best care to be given to all babies born preterm no matter at what gestation, and not just those admitted to intensive care.
"Babies born early are at a higher risk of conditions such as asthma in childhood and should be given regular health check-ups to ensure they remain healthy.
"While the study indicates a slight increase in the risk of asthma and wheezing in children born a few weeks early, we would not suggest this is a cause for concern."
Leanne Metcalf, assistant director of research at Asthma UK, said, as reported by the Press Association: "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."
To increase your baby's chances of a healthy start in life, see our roundup of the best foods to eat during pregnancy...
Benefit To Baby: Healthy Growth Protein is needed to build and repair cells, and is essential to a baby's development and growth. Red meat and dairy are rich in protein, but they're also high in saturated fats. Balance your diet with fish protein (in all fish products), which also contains essential fatty acids. And don't forget vegetable protein, which includes brown rice, quinoa, chickpeas, lentils, baked beans, pumpkin seeds and cashew nuts. A great alternative protein source, tofu is low in fat and will help balance those blood sugar levels. Add to juice from pomegranate and mixed berries for a sweet drink that also packs a powerful antioxidant punch.
Benefit For Mother And Baby: Boost Energy Levels And Provides Nutrition To Baby Iron is vital for your baby's physical growth and brain development, and helps produce the blood required to supply nutrition to the placenta. Not enough iron, and you can feel tired and be more susceptible to infections. There's also a greater risk of premature birth and your baby having a low birth weight.
Benefit To Baby: Brain Development Vitamin B6, also known as pyridoxine, helps your body metabolise protein, fats, and carbohydrates. It also helps form new red blood cells, antibodies, and neurotransmitters, and is vital to your baby's developing brain and nervous system.
Benefit To Mother: Helps Constipation Many pregnant women suffer from constipation, which is cause by an influx of hormonal changes that play havoc with the digestive system. It To avoid discomfort and to help regulate your bowels, eating a rich fibre diet will help get things moving, as they help absorb excess acid and gas, help to speed up digestion and empty your stomach faster. Foods like brown rice, dried figs, kidney beans and avocado are all rich sources of fibre. Pumpkins are great as they offer fibre plus it's said to act like a mild laxative.
Benefit To Mother And Baby: Increases Energy Levels And Bone Building High in calcium (important during pregnancy for building your baby's bones) with a sweet kick from the honey, this treat should tide you over without making you sleepy. Dairy foods provide vitamins A and D, which are essential for bone-building and bone maintenance for you and your baby. They are also a good source of protein.
Benefit to Mother: Eases Heartburn And Water Retention Dried figs are laden with digestive enzymes, which should help you to digest your food and ease those heartburn symptoms. They're also rich in the essential mineral potassium, which helps to maintain the body's fluid balance during pregnancy, which is essential to battling swollen legs, hands and ankles.
Benefit To Baby: Maintains Healthy Nervous System Omega-3 fatty acids are vital for your baby's brain and nervous system, as well as your own mental health. Foods rich in omega-3 include oily fish like fresh tuna, mackerel and sardines, although restrict your intake to twice a week, as too much fish can increase risk of pollutants. Fatty acids help brain development and work to improve its function, so as well as being nutritious, slow-releasing energy snacks, like sesame seeds, which help keep you mentally alert and working well throughout the day.
Benefit To Mother: Alleviates Morning Sickness Ginger has long been associated with alleviating nausea and has been used as a medicine in Asian, Indian, and Arabic herbal traditions since ancient times. In China, for example, ginger has been used to help digestion and treat stomach upset, diarrhea, and nausea for more than 2,000 years. Ginger biscuits are a good food to nibble on when the nausea starts, or sip on ginger tea or suck on ginger flavoured sweets. Peppermint and mint are also great nausea-relieving agents too.
Benefit To Baby: Strengthens Bones Sweet potatoes offer a rich source of folic acid, which helps prevent neural tube defects in foetuses. It also protects your unborn baby from spinal cord problems, such as spina bifida. lentils are also a great for increasing your folic acid intake, as one cup provides 358mcg of folic acid, almost the daily requirement of 400mcg. Fruits like strawberries are a great way to get your folic acid, and even tastier if you dip them in chocolate! Scientists in Finland found that eating chocolate when pregnant resulted in happier, livelier babies, but keep your waistline in mind and be conservative when dipping.
Benefit To Mother: Curbs Food Cravings A handful of almonds and apricots will provide you with a sweet kick that's high in protein - this will help to curb cravings as well as keeping you feeling fuller for longer.
Benefit To Mother: Protects From Pre-eclampsia Parsnips are a good source of fibre and folate (the natural form of folic acid), as well as providing potassium (associated with a lowering in blood pressure) which is vital for protecting against pre-eclampsia, a condition caused by high blood pressure.