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Pregnant woman's stomach.

A new study published today in The British Medical Journal has demonstrated that gestational age at birth is a strong predictor of childhood health outcomes, even up to ten years of age.

Premature birth can have long-term health repercussions, but until now the relationship between gestational age at birth and future childhood health outcomes was unclear. This was investigated by NDPH’s National Perinatal Epidemiology Unit (NPEU) using TIGAR (Tracking the Impact of Gestational Age on health, educational and economic outcomes: a longitudinal Record linkage study); a large-scale cohort study on more than one million children born in England between 2005 and 2006. The children were categorised according to their gestational age by week at birth from less than 28 up to 42 weeks. The children were followed up and the number of inpatient hospital admissions they had was recorded. The average follow-up period for each child was 9.2 years.

During the study period, just over half (525,039) of the children were admitted to hospital at least once, with over 1.3 million admissions in total. After accounting for other potential risk factors (such as mother’s age, marital status and area-based social deprivation, and child’s sex, ethnicity and month of birth), the results showed a strong association between hospital admissions during childhood and gestational age at birth.

Babies born following a full-term pregnancy (at 40 weeks) showed a rate of 28 hospital admissions in infancy per 100 babies – this figure was about 6 times higher in babies born extremely prematurely (less than 28 weeks). By the time the children were aged 7-10 years, they tended to have fewer hospital admissions, but the rate was still about 3 times higher in those born at less than 28 weeks.

But even children born 1 or 2 weeks early had higher admission rates. Compared to those born at 40 weeks, the hospital admission rate in infancy was 10% higher in those born at 39 weeks and 29% higher in those born at 38 weeks.

‘Across all ages and for all gestational ages, the most common cause of hospital admission was infection, especially respiratory infections. This may be caused by very preterm infants having more immature immune systems than their full-term peers, and the fact they are often ventilated at birth which can cause lung damage’ says Dr Victoria Coathup, one of the study’s authors at NPEU.

From age 5, children born very preterm also had significantly more hospital admissions due to central nervous system conditions (such as epilepsy and cerebral palsy), which could be linked to oxygen starvation or trauma during pregnancy or birth. Admissions related to physical injuries were also more common in children born preterm. This may be due to behavioural conditions or impaired cognitive function, which have been associated with premature birth.

These rate differences became smaller as the children grew older, particularly after age 2. This likely reflects the immune systems of the prematurely-born infants eventually starting to catch up with those of the full-term infants. However, an excess risk remained up to age 10, even for children born at 38 and 39 weeks gestation.

‘It is clear from these results that there needs to be a shift away from grouping infants with broad gestational ages together. Instead, gestational age should be treated as a continuum to identify infants most at risk of future complications’ says Professor Maria Quigley, who led the study at NPEU.

TIGAR is a collaboration between the University of Oxford, the University of Leicester and City University London.  The study was funded by a grant from the Medical Research Council.