Pregnancy and child

Growth of newborn babies' brains tracked

"Scans chart how quickly babies' brains grow," reports BBC News Online.

The headline follows a fascinating study that shows newborn babies' brains are about a third the size of an adult's at birth, and rapidly grow to just over half the size of an adult's within three months.

The study involved 87 healthy babies who were given an MRI brain scan within the first week of life. Most then had a second scan after a month, and some had a third scan aged around three months. The researchers measured the size of the different major structures of the brain and calculated the growth rate.

The speed of growth was greatest just after birth, increasing by 1% per day, gradually tailing off to 0.4% per day by 90 days. The baby boys' brains were slightly larger than the baby girls' brains just after birth (347cm3 compared to 335cm3) and had grown slightly faster by 90 days (66% of the size) compared with female brains (63%).

Studies such as this can help our understanding of brain development, which could help unearth abnormal processes and certain developmental conditions. Being able to monitor brain development over time with an investigation that does not appear to have any side effects is also welcome. But this small study can't be used on its own as a reference for what's normal.

Where did the story come from?

The study was carried out by researchers from the University of California, the University of Hawaii and the Norwegian University of Science and Technology.

It was funded by the National Institutes of Neurological Disorders and Stroke, the National Institute on Drug Abuse, and the National Institute on Minority Health and Health Disparities.

A clear conflict of interest was reported by one of the study authors, who is a founder and equity holder in CorTechs Labs – a company selling software that analyses brain volumes from MRI scans and compares these volumes to norms.

The study was published in the peer-reviewed medical journal, JAMA Neurology.

The BBC reported the study accurately.

What kind of research was this?

This was an observational study aiming to plot the brain development of healthy babies using repeated MRI scans.

The researchers say there are usually problems obtaining a useable MRI image for newborn infants because it is hard to get the baby to stay still, head sizes change rapidly during the first few months, and the shape of the head may have been affected by birth.

To add to the difficulties, all of the neurones are already present but squeezed into a third of the size of an adult brain, making images more difficult to interpret.

The researchers wanted to chart normal development in babies who were not distressed by illness and therefore able to sleep during the scan.

This information could provide a benchmark that could help work out how and when all sorts of disorders start to occur, and therefore potentially lead to new treatments. 

What did the research involve?

The researchers gave 87 babies (39 boys and 48 girls) an MRI scan about a week after birth. The scan was conducted while they were asleep, so no sedation was required.

A repeat scan was performed on 57 babies after one month, and 49 of them had a third scan two months later.

The researchers measured the size of the different major structures of the brain and calculated the growth rate.

Data was collected regarding the ethnicity of the child and the mother's medical history and use of medication during the pregnancy.

Babies were excluded from the study if:

  • they had any known neurological disorders or abnormalities 
  • they had any newborn illness requiring more than one week in intensive care
  • there was a brain abnormality
  • they had overt perinatal TORCH infections (toxoplasmosis, other, rubella, cytomegalovirus or herpes simplex) at birth, or a major neurological disorder since birth 
  • there was any chromosomal anomaly
  • there were any other contraindications for MRI studies
  • the mother tested positive for HIV infection 
  • the mother had smoked tobacco cigarettes or had more than three alcoholic drinks a month during the pregnancy

What were the basic results?

The baby boys' brains were slightly larger than the baby girls' brains just after birth (347cm3 compared to 335cm3).

The longer the gestational age, the bigger each section of the brain, apart from the pallidum (an area that may be important in reward and motivation) and the third ventricle (a cerebrospinal fluid-filled area involved in communication between different areas of the brain).

By 90 days, the brains had grown by nearly two-thirds, with male brains growing slightly faster (66%) compared with female brains (63%).

The highest area of growth was the cerebellum at the back of the brain, which controls movement, co-ordination and balance. This had grown by 113% in males and 105% in females.

The slowest area was the hippocampus, which is known to be involved in memory formation – on average, this grew by 47%.

On average, the brains grew from 33.5% of the average size of an adult's brain to 54.9% by 90 days.

The speed of growth was greatest just after birth, at 1% per day, gradually reducing to 0.4% per day by 90 days.

Most of the babies were of mixed race (54%), then native Hawaiian/Pacific islander (22%), Asian (13%), white non-hispanic (8%) and black (1%).

How did the researchers interpret the results?

The researchers reported that they have "accurately mapped out early postnatal whole-brain growth trajectories for male and female infants", which they believe is the first time this has been done.

They say if the study is repeated on a larger and more diverse group of babies, this information could provide a reference point to measure brain growth in babies who have had a brain injury, and for monitoring the effects of any treatments.


This study has mapped out the growth rate of the major structures of the brain in 87 apparently healthy neonates from within a week of birth up to 90 days.

A study of this nature can help our understanding of the growth and development of the brain and our ability to monitor brain development over time. The fact the investigation had no apparent side effects is also welcome.

However, as the authors point out, the relatively small size of the study means the results cannot be used as a reference for normal development. Larger and more ethnically diverse studies would be required.

The goal of establishing data for a reference for normal development ties in with the commercial conflict of interest mentioned earlier, as one of the authors founded a company which sells software that analyses brain volumes from MRI scans and compares these volumes to norms.

Currently, brain growth is estimated using a measuring tape to chart the baby's head circumference over time.

The circumference is compared against established norms, with deviation from the norm a potential indication of problems in development and warranting further investigation.

The MRI technique offers a potentially more accurate way of measuring growth or confirming abnormality of growth.

Assessing every child's brain development through an MRI scan is not practical and is probably not the intended endpoint. So the real use of this developing knowledge and technology appears to be providing some evidence to help establish a reference for what is normal and what is abnormal. This could allow abnormalities to be detected earlier than we can currently.

However, there would still need to be a decision made about which babies should be scanned. This would most likely be those at a higher risk of developmental problems, possibly because of a family history or a traumatic birth or pregnancy.

This study highlights the importance of the first few months of life on brain development. This can be supported, if possible, by breastfeeding a baby.

NHS Attribution