The extent of the differences were unexpected and surprised the researchers. They are part of an emerging picture of changes in the heart, blood vessels and blood pressure of adults born after pregnancies complicated by problems such as preterm birth and pre-eclampsia.
‘We have been surprised by how unique the structure of the heart is in young adults that were born prematurely,’ said Professor Paul Leeson of Oxford University, who led the group of researchers. ‘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.’
The implications for future health or risk of heart disease are unknown, but the differences may help explain other recent findings in adults born preterm. For example, they tend to have higher blood pressure – something that was also observed in the participants in this study – and get tired more easily when exercising.
The researchers want to reassure those who may have been born preterm or parents of new premature babies. They say there is nothing they have discovered that should worry people.
First author Dr Adam Lewandowski, who undertook the study at Oxford University, said: ‘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.’
Professor Leeson added: ‘I think any health message right now is that doctors and those who were born preterm can be aware of the greater chance of higher blood pressure in later life. A very small number may see raised blood pressure levels that become problematic, but there are established ways of managing that.’
Improvements in care for premature babies over the past 20 years mean that now up to one in 10 young adults will have been born before 37 weeks.
The researchers report their findings in the journal Circulation. The study was funded by the British Heart Foundation with additional support from the National Institute for Health Research Oxford Biomedical Research Centre.
The team from the Oxford Cardiovascular Clinical Research Facility, part of the Radcliffe Department of Medicine, used cutting-edge magnetic resonance imaging techniques that have been specifically developed to look at the heart and how well it is performing.
They compared the right ventricles – one of the four main chambers of the heart – of around 102 young adults aged 23–28 who had been born prematurely with a similar group of adults of the same age who had been born at full term. They also scanned the hearts of a further 30 people 10 years older to compare any differences with normal changes seen with age.
The young adults that were born preterm had right ventricles that were smaller and had thicker walls than those who had been born at full term.
The differences were greater for those who had earlier premature births: for each week the pregnancy was shorter, there was a 2.74% relative increase in the mass of the right ventricle.
These results mirror changes seen in the left ventricle for adults who had been born preterm in a previous study by the group published earlier this year. The impact of preterm birth appears to be slightly greater on the right ventricle, however.
In addition, the right ventricles of those born prematurely were pumping a smaller volume of blood than those who had been born at full term. Six of the 102 young adults born prematurely pumped less blood from their right ventricle than the lower limit of what is considered clinically normal.