Karolinska study links premature birth to increased risk of mental health problems

One of the largest studies to investigate birth complications and later mental health has found that premature birth constitutes a single, independent risk factor for a range of severe psychiatric disorders. Researchers at King's College London in the UK and Karolinska Institutet suggest that neurodevelopmental differences in those born prematurely may be important in understanding the link.

Researchers identified all individuals registered in the Swedish birth register between 1973 and 1985 who were alive and living in Sweden at the age of 16, a total of nearly 1.5 million individuals. By analyzing national hospital discharge registers, they identified all individuals admitted to hospital with their first episode of a psychiatric disorder.

The study, published in the Archives of General Psychiatry, found that individuals born extremely prematurely (less than 32 weeks gestation) were 2.5 times more likely to have psychosis as young adults, nearly 3 times more likely to have depression, and 7.4 times more likely to have bipolar disorder than those born at term (37-41 weeks gestation). The findings also revealed a smaller, yet still significant, increased risk of developing bipolar disorder, psychosis and depression for those born moderately prematurely (32-36 weeks).

The study also investigated the link between premature birth, eating disorders and alcohol and drug dependency, but association with these disorders was much weaker. Other adverse perinatal factors including newborn health, maternal socio-demographic characteristics and maternal psychiatric history were taken into account and were found to have no significant effect on the findings.

"We believe that the increased risk of mental disorders in those born very prematurely can be explained by alterations of brain development", says Professor Christina Hultman at Karolinska Institutet, who led the Swedish part of the study. "The immature nervous system in these children is particularly vulnerable to brain injury resulting from birth complications."

Approximately 6 percent of babies in Sweden are born prematurely every year. Thanks to research and new technology, today many of prematurely born can be saved. Most of these babies go on to lead healthy lifestyles, although as a group they are more likely to require extra school support and be hospitalized with a variety of physical problems. Therefore the authors point to the importance of raising awareness of the increased risk of mental health disorders in people born prematurely, and suggest gestational age should be considered when investigating risk factors for psychiatric disorders in young adults.

Study leader was Chiara Nosarti at the Institute of Psychiatry, King's College London. The study was funded by a National Alliance for Research on Schizophrenia and Depression (NARSAD) Brain and Behavior Research Foundation and supported by the National Institute of Health Research (NIHR) Biomedical Research Centre for Mental Health at the South London and Maudsley NHS Foundation Trust and the Institute of Psychiatry, King's College London.