Health consequences of premature birth revisited – what have we learned?

The survival of prematurely born babies is, to a large extent, a modern phenomenon over the last 20–30 years, and it reflects improvements in obstetric routines and neonatal care. A growing number of children now survive into early adulthood, and this has been the focus of a number of follow-up analyses on somatic and mental health outcomes, as well as psychological scoring. As the incidence of prematurity in a country such as Sweden is 6%, according to the Swedish Medical Birth Register (accessed 4 May 2017), an accumulation of survivors has now reached early adulthood. Previous fears for poor health conditions in general following premature birth have not been supported, as documented by systematic reviews. In this issue of Acta Paediatrica, Raju et al. summarised the updated evidence on prematurity and health, based on a number of reports and systematic reviews [1]. They concluded that even if the risk of some adverse health consequences had increased following premature birth, the general impression was that the prognosis had improved for each extra gestational week and that this was a reflection of the better standards of medical care that are now offered.

It is also of special interest to elucidate on the mechanisms behind the link between prematurity and, for example, increased cardiovascular risk. Studies by Bonamy, later Edstedt Bonamy et al. investigated the vascular structure and arterial wall morphology in prematurely born children and compared them to children born at term [2, 3]. They reported that carotid artery elasticity and structure were not altered after preterm birth [2]. A further finding was that very preterm birth, as well as exposure to maternal smoking in foetal life, was independent and strong risk factors for general aortic narrowing 15 years after birth [3]. Other authors have found that children born preterm were characterised by decreased elastic properties of the descending abdominal aorta, which were potentially attributable to the impaired viscoelastic properties of the aorta and lipid damage [4]. A Canadian group reported that transient neonatal high oxygen exposure led to vascular wall alterations, namely a decreased elastin/collagen ratio and a shift in the balance towards increased deposition of collagen, which were associated with increased rigidity. It is important to note that such changes are present before the elevation of blood pressure and vascular dysfunction [5], and this could increase the risk of arterial stiffness and vascular ageing in adult life.

Regarding blood pressure regulation, prematurity has been linked to increased blood pressure and to reduced capillary function, which was linked to specific biomarker profiles [6]. This could contribute to an increased cardiovascular risk in prematurely born infants and would remain invisible until they reached middle age. Taken all together, these findings could be of importance for long-term cardiovascular risk increases.

So what should be done, based on the facts and their implications from the present systematic review? First of all, these prematurely born children and their parents should know that the prognosis has improved considerably over recent years and that previous interventions that imposed risk, such as too much oxygen in premature newborns with the risk of retinal damage, have now been abandoned.

Furthermore, it has been suggested that the increased cardiometabolic risk of young adults born either prematurely or small for gestational age (SGA) could encourage clinicians to provide structured follow-up appointments at polyclinics, offering cardiovascular risk factor screening and treatment starting in young adulthood. This could prove to be important on an individual level for controlling risk, but also provide a way to strengthen the links between paediatrics and adult medicine.

The previous grim prognosis for babies born prematurely has now improved substantially, with better survival and less immediate health hazards, even if these should not to be disregarded or overlooked [7]. Well-designed clinical cohorts not only warrant follow-up periods that last decades, but they should also be repeated as neonatal medical care improves. Similarly, studies to identify and treat some of the important causes of preterm deliveries, such as pre-eclampsia, also warrant long-term follow-up studies to elucidate lifelong results and safety for the mother and child [8-10]. National registers on health-related factors that add data to previous studies might be cost-effective tools to complement these clinical studies. On the other hand, the improved survival into adult life that has already been achieved for preterm born children is an impetus for establishing routines to screen and treat cardiovascular risk factors in this group, by applying a life course perspective from early life to adulthood.