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Low birthweight linked to higher mortality right up to adolescence

Act against risk factors for low birthweight, to reduce numbers of vulnerable babies

Louise Prime

Wednesday, 11 May 2016

Children born underweight in England and Wales have a much higher risk of mortality right up until they reach adulthood, compared with children born at a healthy weight, UK research* has shown.

The study, published in PLOS Medicine, showed that the relative risk of death during infancy was 145 times higher for babies born at very low birthweight, and was still more than six times higher during childhood and adolescence. Its authors said that to reduce the rate of delivery of such vulnerable babies – and thus later mortality – it is important to act against risk factors for low birthweight, such as maternal smoking and deprivation.

A research team from the University of Cardiff, funded by the Welsh Government, compared death rates throughout infancy and childhood for more than 12 million children born between 1993 and 2011 in England and Wales. They classified the children by four birthweight groups: very low birthweight (VLBW, <1.5kg), low birthweight (LBW, 1.5kg to <2.5kg), and two groups of appropriate birthweight, 2.5 to <3.5kg and ≥3.5kg.

During infancy (<1 year old), VLBW babies were 145 times more likely to die than babies born at ≥3.5kg; for LBW babies the hazard ratio (HR) was 9.8. The most common causes of death for these babies were perinatal events (which accounted for 84% of deaths in VLBW babies) and congenital malformations.

But even those underweight babies who survived their first year remained at a relatively elevated risk of dying. The HR for dying during childhood and adolescence (1-18 years old) was 6.6 for VLBW babies, and 2.9 for LBW babies, relative to children born at ≥3.5kg. Leading causes of death after one year old in the VLBW group were conditions of the nervous system (20% of deaths) and respiratory system (16%); in the LBW group, cancers and external conditions (including accidents) each accounted for 20% of deaths.

The authors said that although their study couldn’t take account of possible confounding factors such as gestational age and maternal smoking, it benefited from being large, population-wide and having long follow-up, and including cause-of-death data.

They concluded: “By understanding and ameliorating the influences of upstream exposures such maternal smoking and deprivation, later mortality can be decreased by reducing the delivery of vulnerable infants with LBW.”

* Watkins WJ, Kotecha SJ, Kotecha S. All-cause mortality of low birthweight infants in infancy, childhood, and adolescence: population study of England and Wales. PLOS Med 2016 13(5): e1002018. doi:10.1371/journal.pmed.1002018.

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