Babies born at an extremely low birth weight have higher odds of developing psychiatric problems than babies born at a normal birth weight, but are less likely to abuse drugs or alcohol, according to new Canadian research.

Researchers at McMaster University in Hamilton, Ont., studied 84 adults who were born weighing less than 1,000 grams (2.2 pounds) and 90 adults who were born at normal birth weight. All were born in Ontario between 1977 and 1982, and were followed from birth with regular assessments.

The researchers found that the adults who were born weighing less than 1,000 grams were two-and-a-half times less likely to develop an alcohol or substance use disorder than those born at normal birth weight.

However, the low birth weight babies had a two-and-a-half times increased risk of developing a “clinically significant psychiatric problem” as adults compared to normal birth weight babies. These included depression, an anxiety disorder, or attention-deficit/hyperactivity disorder (ADHD).

The risk was even higher for babies born at extremely low birth weight who were also small for their gestational age, meaning they were in the less than 10th percentile for weight. 

And the low birth weight babies whose mothers received a full course of steroids before giving birth were nearly four-and-a-half times more likely to develop a psychiatric problem, and did not have a lower risk of developing alcohol or drug use disorders.

Lead study author Dr. Ryan Van Lieshout, assistant professor of psychiatry and behavioural sciences at the Michael G. DeGroote School of Medicine at McMaster, said Monday that despite the increased risks, “not even a majority of these extremely low birth weight survivors will develop psychiatric disorders.”

And it remains unclear whether the steroids are responsible for the increased risks in babies exposed to the drugs, he said.

“The results of this study are very preliminary because we’re the first group to report the results of the steroids in babies this small,” Van Lieshout told

“But I wouldn’t want women to get the message that they don’t want to get the steroids (because) they are afraid their child will have a mental health problem later in life.”

Steroids are “very important medicines” for mothers to receive when they are threatening preterm labour, he said, because they are associated with a decreased risk of serious brain and lung problems, as well as death, in babies.

The findings were published Monday in the journal Pediatrics.

In their study, the authors note that advances in health care have allowed more babies born at extremely low birth weight to survive into adulthood. Previous research has suggested that these infants are at an elevated risk of developing psychiatric disorders in childhood and adolescence, particularly ADHD and social difficulties.

And studies of infants born at very low birth weight, which is less than 1,500 grams, may be at an elevated risk for developing ADHD, mood and anxiety disorders and other social problems in their twenties. This group is also less likely to have alcohol or substance abuse disorders.

But little is known about the mental health statuses of adults in their thirties who were born at an extremely low birth rate. What is also unclear is whether extremely low birth rate or steroid exposure in the womb increase the risk of developing mental health problems.

In their report, the researchers say that babies born at extremely low birth weight may be at lower risk of developing substance abuse problems for a number of reasons, including having more cautious or risk-avoidant personalities, or the fact that their parents monitored them so closely earlier in life.

As for the increased risk of developing a psychiatric disorder, the contributing factors are likely “complex,” they write.

“These factors include prenatal insults leading to preterm birth and exposure to stressful neonatal experiences, both of which could lead to brain changes,” they write.

And, the researchers note, the study is the first to show that extremely low birth weight babies exposed to a complete course of steroids are not only not protected against substance abuse disorders, but have higher odds of developing a psychiatric disorder.

Preterm babies typically have changes in parts of their brains involved with memory, organization and stress responses, according to Van Lieshout. It could be that as the steroids cross the placenta and bind to receptors in those parts of the brain, it leads to emotional or behavioural changes.

“It could be that they may already have vulnerable brains and then perhaps these steroids-- although they really help the lungs and other parts of the brain-- may be interacting with these changes that are already present to produce behavioural changes, or emotional, psychological changes,” Van Lieshout said.

“But it’s important to say that that’s a bit speculative.”

Van Lieshout says the findings must be replicated in a much larger sample size before scientists can determine what is causing the mental health problems as these babies grow up.

And it’s important to note that other factors can lead to mental health problems in offspring, including the mother’s own health problems, which can include mental health challenges and socioeconomic factors.

In their conclusion, the researchers do not call for doctors to stop using steroids in a situation where a preterm birth is threatened, noting that it is a “lifesaving intervention.” Rather, they recommend closely following babies exposed to steroids.

“Individuals who are born prematurely and their family members don’t have to worry that their child is absolutely going to develop a mental health problem later in life, because most of them don’t,” van Lieshout said.

But they should bring any concerns to their family doctor so any problem can be detected and treated early.