'Surprising Findings' About Preterm Birth, Mental Illness Link

Megan Brooks

October 02, 2013

Only some psychiatric disorders that have been previously linked to preterm birth are actually caused by early birth, whereas others appear to be related to genetics, new research suggests.

In the largest study of its kind to date, researchers confirmed the strong link between preterm birth and the risk for autism and attention-deficit/hyperactivity disorder (ADHD).

However, they also found that other problems that have previously been closely linked to preterm birth, including severe mental illness, learning problems, suicide, and economic woes, may instead be more closely related to other conditions that family members share.

"Interventions and preventative efforts aimed at lowering the prevalence of preterm birth are essential. But our results also suggest that families where one child is born preterm need wraparound services because all of the offspring in such families need assistance," Brian D'Onofrio, PhD, associate professor in the Department of Psychological and Brain Sciences at Indiana University Bloomington, told Medscape Medical News.

The study was published online September 25 in JAMA Psychiatry.

Surprising Findings

Previous studies linking preterm birth to various mental illnesses have been unable to rigorously examine whether the reported associations are caused by confounding factors rather than the harmful effects of being born preterm, the researchers note.

To get a better handle on the extent to which the reported associations may or may not be the result of confounding factors, they used a "quasi-experimental" sibling-comparison design and controlled for statistical covariates that varied within families.

The investigators identified all individuals born in Sweden from 1973 to 2008 (3,300,708 offspring of 1,736,735 mothers) and linked them with various outcomes through 2009.

They report that compared with term birth, preterm birth was associated with greater risk for infant mortality, autism, and ADHD, independent of shared familial confounding factors and statistical covariates, "consistent with a causal inference," the researchers say.

In contrast, associations between preterm birth and other outcomes, namely, schizophrenia, bipolar disorder, suicide, and some academic and social problems, were either greatly or completely attenuated in fixed-effects models, suggesting that confounding factors, such as environmental factors, are involved.

This suggests, Dr. D'Onofrio said, "that part of the association with severe mental illness and all of the association with suicide isn't due to preterm birth; it is due to something else, something that siblings share."

"We were surprised by these latter findings because they are not consistent with other studies," Dr. D'Onofrio told Medscape Medical News.

According to the World Health Organization, in both developing and industrialized countries, more than 1 in 10 children are born prematurely, and the numbers are growing.

"Our study," Dr. D'Onofrio said, "is part of a growing interest in research and public health initiatives focusing on very early risk. When you look at early risk factors, they don't just predict 1 type of problem; they frequently predict lots of problems with long-term implications."

They hope their findings will inform "etiologic theory, risk assessment, and follow-up practices to prevent adverse outcomes associated with preterm birth."

The research was supported by grants from the National Institute of Child Health and Human Development, the National Institute of Mental Health, the Swedish Research Council, and the Swedish Prison and Probation Services. The authors have disclosed no relevant financial relationships.

JAMA Psychiatry. Published online September 25, 2013. Abstract

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