Young adults who were born prematurely often have smaller hearts with thicker walls, which can lead to cardiovascular problems later in life.

"We have been surprised by how unique the structure of the heart is in young adults that were born prematurely. They have smaller hearts, thicker walls and pump a smaller volume of blood on average than young adults who were born after a full-length pregnancy," Professor Paul Leeson of Oxford University, who led the study, said, according to an Oxford University press release.

The long-term health effects of this finding are yet to be determined, but studies have shown those born preterm usually get tired quicker while exercising and have higher blood pressure than people who had a healthier birth.

"The people who took part in our study are young people still in their twenties, and they clearly don't have heart disease. We have been able to identify these differences because of the sophisticated ways we have developed to image the heart. The science behind why this may be occurring in those born preterm is fascinating and should help us understand why some people may develop heart problems in later life and some do not," first author Dr. Adam Lewandowski, said.

The survival rate of premature babies has increased over the past 20 years thanks to better medical care. Today one in 10 young adults were born at 38 weeks or earlier.

The team used magnetic resonance imaging techniques to compare the heart structures of 102 people between the ages of 23 and 28 who had been born prematurely with a similar group that had not.

They also scanned the hearts of a smaller group that was about 10 years older to see what changed.

"For each week the pregnancy was shorter, there was a 2.74 percent relative increase in the mass of the right ventricle," the press release stated.

The group that had been born prematurely often pumped less blood from their right ventricle than the control group.

"We are trying to dig deeper into what's different about the hearts of those born preterm," Adam Lewandowski, first author of the study, said, according to Medical News Today. "The potential scientific explanations for why their hearts are different are fascinating and our study adds to the growing understanding of how premature birth shapes future heart health."

Other long term problems associated with premature birth include: cerebral palsy, hearing and vision problems, psychological problems, dental problems, and other chronic illnesses, according to Mayo Clinic.