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13-09-2010 | Mental health | Article

Birth weight linked to mental illness risk

Abstract

Free abstract

MedWire News: A low birth weight is associated with an increased risk for schizophrenia and other mental illnesses, research shows.

"The exact nature of the relationship between birth weight and risk of schizophrenia in adulthood has been debated frequently in the literature but remains unresolved," explain Kathryn Abel (University of Manchester, UK) and team.

"Most earlier studies have explored the link between low birth weight (<2500 g) specifically and schizophrenia but have not established this relationship. Moreover, little is known about its relationship with birth weight across the normal range," they add.

To investigate further, and to examine whether low birth weight is linked to other mental illnesses in adulthood, the researchers studied birth weight data on 1,491,467 individuals born in Sweden and Denmark between 1973 and 1986.

Examination of national psychiatric treatment registers revealed that 5445 of these individuals had developed schizophrenia and 57,455 had developed any adult psychiatric disorder by 2005.

After accounting for year of birth, gender, presence of maternal psychiatric disorders, and social class, the researchers found that individuals with a birth weight of less than 2500 g were between 1.26 and 1.63 times more likely to develop schizophrenia than the general population, with lower birth weight associated with increased risk.

However, the risk for schizophrenia was not confined to individuals with a birth weight of less than 2500 g, with a significant linear trend of increasing odds ratios with decreasing birth weight across the birth weight range, and this trend was similar for all psychiatric disorders.

The researchers also found that being small for gestational age (defined as being more than two standard deviations less than the normal birth weight for a particular gestational age) was significantly associated with an increased risk for any psychiatric diagnosis (odds ratio [OR]=1.35) and schizophrenia (OR=1.34). Low gestational age (less than 37 weeks) was also associated with any psychiatric diagnosis (OR=1.25) and schizophrenia (OR=1.34).

Abel and team comment in the Archives of General Psychiatry: "In by far the largest sample to date, we have shown that low birth weight is associated with increased risk for adult schizophrenia.

"In contrast to those previous studies that have focused on birth weight less than 2500 g, however, we provide evidence that there is no threshold of effect for low birth weight but that risk extends into the normal birth weight range. We also report that other disorders severe enough to result in psychiatric admission or attendance at an outpatient clinic show a similar pattern of a graded association with birth weight."

They conclude: "Future research into the prenatal causes of adult mental disorder should place greater emphasis on the broader links between fetal growth, its control, and brain development."

MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Mark Cowen

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