London, Nov 26 (IANS): Researchers have found that being born early is associated with a higher risk of hospital admission throughout childhood than being born at full term.

Existing evidence suggests that the risk of illness associated with preterm birth declines as children grow up, but it remains unclear at what age this begins to happen and how these changes vary by week of gestational age at birth.

For the study, published in the journal 'The BMJ', a team of UK researchers set out to examine the association between gestational age at birth and hospital admissions to age 10 years and how admission rates change throughout childhood.

Their findings are based on data from more than one million children born in NHS hospitals in England between January 1, 2005 and December 31, 2006.

Children were monitored from birth until March 31, 2015 (an average of 9.2 years per child), during which time the researchers analysed numbers of hospital admissions.

Gestational age at birth was analysed in weeks, from less than 28 up to 42 weeks.

Over 1.3 million hospital admissions occurred during the study period, of which 8,31,729 (63 per cent) were emergency admissions. Just over half (5,25,039) of children were admitted to hospital at least once during the study period.

After taking account of other potentially influential risk factors, such as mother's age, marital status and level of social deprivation, and child's sex, ethnicity and month of birth, the researchers found that hospital admissions during childhood were strongly associated with gestational age at birth.

The hospital admission rate during infancy in babies born at 40 weeks was 28 per 100 person years -- this figure was about six times higher in babies born extremely prematurely (less than 28 weeks).

By the time the children were aged 7-10 years, the hospital admission rate in children born at 40 weeks was seven per 100 person years -- this figure was about three times higher in those born at less than 28 weeks.

But even children born a few weeks early had higher admission rates.

Being born at 37, 38, and 39 weeks' gestation was associated with a difference in the rate of admission of 19, nine, and three admissions per 100 person years during infancy, respectively, compared with those born at 40 weeks.

The risk of hospital admission associated with gestational age decreased over time, particularly after age two. However, an excess risk remained up to age 10, even for children born at 38 and 39 weeks' gestation.

"Infections were the main cause of excess hospital admissions at all ages, but particularly during infancy. Respiratory and gastrointestinal conditions also accounted for a large proportion of admissions during the first two years of life," the study authors wrote.