To investigate third-trimester extrauterine brain growth and correlate this with clinical risk factors in the neonatal period, using serially acquired brain tissue volumes in a large, unselected cohort of extremely preterm born infants.

Preterm infants (gestational age <28 weeks) underwent brain magnetic resonance imaging (MRI) at around 30 weeks postmenstrual age and again around term equivalent age. MRIs were segmented in 50 different regions covering the entire brain. Multivariable regression analysis was used to determine the influence of clinical variables on volumes at both scans, as well as on volumetric growth.

MRIs at term equivalent age were available for 210 infants and serial data were available for 131 infants. Growth over these 10 weeks was greatest for the cerebellum, with an increase of 258%. Sex, birth weight z-score, and prolonged mechanical ventilation showed global effects on brain volumes on both scans. The effect of brain injury on ventricular size was already visible at 30 weeks, whereas growth data and volumes at term-equivalent age revealed the effect of brain injury on the cerebellum.

This study provides data about third-trimester extrauterine volumetric brain growth in preterm infants. Both global and local effects of several common clinical risk factors were found to influence serial volumetric measurements, highlighting the vulnerability of the human brain, especially in the presence of brain injury, during this period.