Premature brains develop differently in boys and girls

New research shows effects of prematurity to be more severe for male brains than female brains.

Brains of baby boys born prematurely are affected differently and more severely than premature infant girls’ brains, according to a new study by researchers in the University of Iowa Carver College of Medicine. The study, published Sept. 19 in the journal Pediatric Research, analyzed magnetic resonance imaging (MRI) brain scans from an ongoing study on premature babies to examine how the brains of baby boys and girls changed and developed.

The study was led by Amanda Benavides, MD, PhD, a postdoctoral scholar in psychiatry, and Peg Nopoulos, MD, professor and chair of psychiatry, and a member of the Iowa Neuroscience Institute.

The researchers used high-quality MRI scans of the brains of 33 infants, including babies who were full term (born at least 38 weeks) and preterm infants (born at less than 37 weeks). Information about brain structure obtained from the scans was combined with information gathered from questionnaires completed by the infants’ mothers and other data collected when the babies were born.

“The window between birth and one year of age is the most important time in terms of brain development. Therefore, studying the brain during this period is important to better understand how the premature brain develops,” Benavides explains.

Brain measurements taken from the MRIs showed that even at this very young age, there are major sex differences in the structure of the brain, and these are independent of the effects of prematurity. Brain tissue is divided into cerebral gray matter, which includes regions of the brain that influence muscle control, the senses, memory, speech, and emotion, and cerebral white matter, which helps to link different regions of grey matter to each other. While boys’ brains were overall larger in terms of volume, girls had proportionately larger volumes of gray matter and boys had proportionately larger volumes of white matter. These same sex differences are seen in older children and adults, and therefore the study documents how early in life these differences are seen. 

When looking at the effects of prematurity, the researchers found that the earlier a baby was born, the smaller the overall cerebral volume. However, the effect of prematurity on gray matter and white matter was different depending on a baby’s gestation age in conjunction with its sex. The earlier a baby boy was born, the lower the researchers found his cortex volume (gray matter) to be. The earlier a baby girl was born, the lower was the volume of white matter in her brain. Overall, although the effects of prematurity were seen in both boys and girls, the changes in the brain due to prematurity were more abnormal in boys than in girls.

Previous research has shown that male fetuses are more vulnerable to developmental abnormalities, and that this could lead to other unfavorable outcomes. Findings from the current study now add to this by showing how the brains of baby boys born too early are affected differently to that of baby girls.  

“Given this background, it seems likely and even expected that the effects of prematurity on brain development would be more severe in males. The insults to the premature brain incurred within the first few weeks and months of life set the stage for an altered developmental trajectory that plays out throughout the remainder of development and maturation,” Nopoulos says.

Reference: Benavides, A. & Metzger, A. et al (2018). Sex Specific Alterations in Preterm Brain, Pediatric Research

Note to Editors: This release is adapted from a release issued by Pediatric Research.