Long term magnetic resonance imaging : follow up after preterm birth

Abstract

Background: Since the introduction of neonatal intensive care units, the survival after preterm birth has improved drastically and development after preterm birth has become an area of intense research. Many studies have found increased rates of neonatal and long term morbidity. In particular, preterm birth has been identified as a risk factor for cognitive and structural brain development and cardiovascular diseases. However, it is also appreciated that the outcome after preterm birth depends on antenatal, neonatal and postnatal care.

Aims: The aims of these studies were twofold: to use a range of MRI imaging techniques to investigate whether preterm born children and adolescents show differences in structural brain and aortic development as well as to compare these results to those reported from other countries, involving similar cohorts.

Subjects & Methods: The volunteers of interest in these studies were participants in the Stockholm Neonatal Project, which was initiated in 1988 as a prospective follow up study and included preterm infants if their weight at birth was less than or equal to 1500g. At 5½ years of age a group of term born children were selected as a control group. In a pilot study (Paper V) a subgroup of these individuals were examined. Papers I IV involve those 74 out of 182 ex preterm and 69 out of 125 control adolescents that were willing to participate. The participants underwent cranial MRI examinations at the MR Center at the Karolinska University Hospital to collect 3D anatomical images and diffusion tensor imaging data. In a subgroup of individuals, images were also collected of the descending aorta.

Results: In all studies we found preterm birth to be a risk factor for long term development. Ex preterm adolescents possessed more structural brain abnormalities mostly in the form of gliosis and white matter loss (Paper I). Their grey and white matter volumes were also lower with the most preterm showing the largest deviations from that of control adolescents (Paper II). Ex preterm adolescents also possessed large areas of thinner cortex (Paper III), hindered white matter microstructure (Papers II and V) and smaller diameters within their descending aortas (Paper IV).

Discussion: While these findings are not unprecedented, we found that with respect to brain the severity and extent of these findings was milder than that based on similar cohorts. It may be that the care provided to the preterm infants in the prenatal and neonatal periods resulted in these relatively moderate findings. Should that be the case, it is hopeful that further research will identify the appropriate care such that preterm born individuals may one day develop identically to those born at term.