Some Conditions Linked to Preterm Birth Not Caused by Preterm Birth Itself

A new study has found that not all problems associated with preterm birth are necessarily caused by preterm birth itself. Instead, some problems may be the result of confounding factors.

“Previous studies have shown that preterm birth is associated with risk for early death, as well as for psychiatric, academic, and social problems,” said Brian M. D’Onofrio, PhD, associate professor in the department of psychological and brain sciences of Indiana University-Bloomington. “Yet, the previous research has been unable to examine the degree to which these associations are actually caused by preterm birth or are due to other factors that are correlated with preterm birth.”

D’Onofrio and colleagues examined this topic further by conducting a population-based cohort study of more than one million mothers and 3 million of their offspring taken from Swedish registries between 1973 and 2008. Using a sibling-comparison approach and considering a broad continuum of premature gestational ages, the study examined the associations between preterm birth and mortality, psychological health, educational outcomes, and social functioning.

“We found that preterm birth was associated with many outcomes, such as infant mortality and autism, even when comparing siblings where one was born preterm and one was not,” D’Onofrio said.

Results indicated that infants born at 23 to 27 weeks gestation had an increased risk for infant mortality (odds ratio, 288.1), autism (hazard ratio [HR], 3.2), low educational attainment (HR, 1.7), and social welfare benefits (HR, 1.3) compared with offspring born at term.

“The findings provide support for the theory that preterm birth has a causal influence on these outcomes,” D’Onofrio said. “However, for other outcomes, such as suicide attempt and educational attainment, our findings suggest that preterm birth itself does not causally influence these problems.”

The association between preterm birth and severe mental illness, such as schizophrenia or bipolar disorder, was greatly reduced when comparing the risk in preterm infants and their siblings. Both siblings had higher chances of severe mental illness than the general population.
 
In addition, although individuals born preterm are more likely to attempt suicide than unrelated individuals who were not born preterm, no distinction existed between siblings. According to the researchers, this finding suggests that “shared familial confounding factors account for the statistical association in the population.”

“Our results indicate that interventions and preventative efforts aimed at lowering the prevalence of preterm birth are essential,” D’Onofrio said. “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.”

Pertinent Points:
- Preterm birth increased the risk of infant mortality and autism.
- Some other academic and social outcomes associated with preterm birth may be caused instead by confounding factors.

References:

D’Onofrio BM, Class QA, Rickert ME, et al. Preterm birth and mortality and morbidity: a population-based quasi-experimental study.

JAMA Psychiatry.

2013 Sep 25. doi: 10.1001/jamapsychiatry.2013.2107. [Epub ahead of print]