The study does confirm the strong link between preterm birth and the risk of infant and young adult death, autism and ADHD. However, it suggests that other problems such as severe mental illness, learning problems, suicide and economic woes, may be more closely related to other conditions shared throughout the family.
“The study confirms the degree to which preterm birth is a major public health concern and strongly supports the need for social services that reduce the incidence of preterm birth,” said lead author Brian D’Onofrio, Ph.D., associate professor in the Department of Psychological and Brain Sciences at Indiana University Bloomington.
“Yet, the findings also suggest the need to extend services to all siblings in families with an offspring born preterm. In terms of policy, it means that the entire family, including all of the siblings, is at risk.”
The study, published in JAMA Psychiatry, is thought to be the largest population-based study of preterm births to date. The researchers analyzed records of 3.3 million children born in Sweden between 1973 and 2008.
Using a sibling-comparison approach, the study examined the associations between preterm birth and mortality, psychological health, educational outcomes and social functioning.
“The study has given us insights that no other study has been able to do,” D’Onofrio said.
The sheer number of children in the study led to meaningful insight into conditions that are relatively rare. For example, birth at 25 to 30 weeks is a rare event, as is autism or schizophrenia. Other studies have not had a large enough pool of information to consider such issues at the same time.
The difficulties that previous studies comparing preterm infants to unrelated non-preterm infants, D’Onofrio said, “is that preterm birth is associated with a lot of other factors that are also predictive of poor outcomes in the offspring. So you are not sure if preterm birth or all these other factors actually cause these harmful outcomes. Trying to tease apart what is due to preterm birth or everything that goes along with preterm birth is very difficult.”
Comparing siblings is a way of controlling for and holding constant everything those siblings share: mothers and fathers, socioeconomic status, and some genetic factors.
“You get the exact same results when comparing differentially exposed siblings and cousins, which suggests our conclusions are very robust,” D’Onofrio said.
When the researchers reviewed infant and young adult mortality, the findings were the same when comparing siblings as when they compared preterm infants to unrelated non-preterm individuals.
Early gestation is associated with greater risk of mortality, suggesting preterm birth has a causal influence. For autism and ADHD, the results are the same with both methods.
In other areas, however, the results are strikingly different from the findings of prior studies. The link between preterm birth and severe mental illness, such as schizophrenia or bipolar disorder, dropped significantly when comparing siblings. Both siblings had a greater chance of severe mental illness than the average person.
For suicide, the findings are even more significant. Although individuals born preterm are more likely to attempt suicide than unrelated individuals who were not born preterm, no distinction was found between siblings.
This suggests, 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.”
“Our study is part of a growing interest in research and public health initiatives focusing on very early risk,” D’Onofrio said. “When you look at early risk factors, they don’t just predict one type of problem; they frequently predict lots of problems with long-term implications.”
Source: Indiana University Bloomington