The weeks and months after a baby is born are a critical time for the growth of the heart of premature babies. This is largely because they are faced with major blood flow changes and increased oxygen demands as they transition to the outside environment during a time where they would normally be developing inside their mother.
A lot of research has identified preterm birth (born before 37 weeks gestation) as a risk factor for developing early heart disease, including heart failure. Heart failure is when the heart can’t pump blood around your body as effectively as it should.
Several studies have shown that preterm birth is linked to abnormalities in the structure and function of their heart, yet the extent and evolution of these changes throughout development, from birth to adulthood, are not well defined. However, it’s important that they are defined as one in ten people worldwide are born preterm.
In our latest study, we performed a meta-analysis of data from published studies that compared the heart’s structure and function using echocardiography or cardiovascular magnetic resonance imaging for people born preterm versus those born at term. We included 32 studies in our analysis, with comparisons between groups made in newborns, infants, children, adolescents and young adults.
The results of our study showed that the left and right pumping chambers of the heart, known as the ventricles, are smaller across all developmental stages in people born preterm. Also, the right ventricle’s contractile pump function is impaired across all developmental stages.
Although the left ventricle’s ability to relax and fill with blood was found to be lower in preterm newborns, this appears to worsen with age. Also, the level of thickening of the left ventricle’s muscle wall from childhood to adulthood is accelerated in people born preterm. Many of these changes were shown to be worse in those born the earliest or most prematurely.
These changes in the hearts of people born preterm have been linked to developing heart disease in later life, but may also put them at more immediate heart disease risk than their term-born peers. Studies show that these physical changes in the heart make people born preterm less able to cope with physiological stress demands, such as exercise.
A lot still to be learned
The reason for these changes are not known. Work from different animal models of preterm birth, including in sheep, pigs and rats, has shown that a likely reason is the early transition from the womb. This is believed to be because the heart undergoes flow and pressure changes around the time of birth, as well as major shifts in oxygen levels (which are much higher outside the womb), causing changes to cells and the shape of the heart.
Ultimately, this results in the heart muscle cells, known as cardiomyocytes, growing differently (switching from rapid division, known as hyperplasia, to increasing cell size, known as hypertrophy) and the structural and functional properties of the heart to change in order to meet the body’s demands. While this is a normal event for all births, the immature preterm heart appears to be less able to cope with these changes, with harm seen at a cellular and structural level.
Given that such a large proportion of the population is born preterm, steps should be put in place to maintain and promote long-term heart health. This includes further research into the best strategies for newborn and infant care to promote healthy heart development, such as early feeding and best practices to support normal lung function, including mechanical ventilation using a machine to move air in and out of the lungs (invasive) and CPAP to provide air through a mask (non-invasive). It also includes lifestyle approaches, such as exercise and nutrition, beginning as early as childhood.
Adam Lewandowski receives funding from the British Heart Foundation.