The fact that the health of premature babies can be rather fragile is well known. Now it appears that preterm birth can also affect the cognitive abilities, at least on the statistical level.

The baby is considered premature is he or she is born before the 37th week of gestation.

Preemies are known to have a greater risk of delays in development, cerebral palsy, hearing and seeing problems. The earlier a baby is born the greater those risks are. The main cause of premature birth is usually not known. Risk factors include hypertension, diabetes mellitus, vaginal infections, psychological stress, obesity, being pregnant with more than one baby, cigarette smoking and usage of drugs such as cocaine and methamphetamine.

Worldwide more than 11% of all infants are born prematurely. This is approximately 15 million births per year. Worryingly, the rate of premature births is rising. From 1990 to 2010 the ratio of prematurely born babies increased from 7.2% to 8.6%.

Based on the previous studies which indicated that brain injury caused by preterm birth can cause learning difficulties and may result in underachievement at school, researchers from the University of Warwick have linked the premature birth with low wages and professional success in the future. They found a relation between being prematurely born and lower IQ, problems with reading and, in particular, decreased mathematical ability, which can have effect on earnings during the adulthood.

The study examined data from more than 15,000 individuals from two large studies. The first one was the National Child Development Study that followed children born in 1958, and the second one was British Cohort Study that followed children born in 1970. Researchers have followed up these two groups of children through to adulthood. Prematurely born participants were compared with participants who were born full-term. This study showed that participants who were prematurely born had a number of inequalities in employment and wealth. The results were as follows:

The percentage of manual workers among the adults born prematurely was higher compared to adults born full-term (32.5% and 25%, respectively). The unemployment rate among them was also higher – 3.3% compared to 2.5% in the adults born full-term. Finally, family income below average was seen in 57.6% of prematurely born individuals compared to 49.1% of individuals born full-term. Similar results were found in the 1958 cohort study.

Around 10-15% of preterm infants show a variety of neurodevelopmental difficulties during infancy, and 30–40% have minor behavioral, motor and learning disorders at school age. Although imaging studies have indicated certain damage of white matter in the brain which may be the cause of neuromotor problems in the perinatal period, the cause of the learning and behavioral difficulties at later age is not so clear.

Some studies of school children showed an association between height, head circumference and intelligence, but it is not clear if it is causal. Poor postnatal growth could be linked with prenatal factors, perinatal illness, drugs, inappropriate nutrition, or following childhood illness or diet. It can also be that only poor growth during some of the critical periods has an effect on future cognitive and behavioral development.

In human development, the late intrauterine and early postnatal periods can be characterized by high growth speed, especially of the brain. In older children, the size of the brain is largely related to the cognitive functions, as is the height. The head circumference correlates well with the volume of brain and so it can be used as a measure of brain growth. Head size at birth has a small correlation with later intelligence, so it has been suggested that postnatal growth failure rather than prenatal problems leads to a smaller head later. The studies proved that growth rates both in infancy and early childhood were related to the IQ but in childhood the effect was greater.

There are many factors that can influence the neurodevelopmental outcomes, but there is no exact mechanism identified so far that can explain all known facts. Some hypothesize that maternal illness can injure immature organs and systems of baby and thus influence the fetal growth through infection and inflammation. Inflammatory mediators such as pro-inflammatory cytokines (such as IL-6 which stimulates secretion of glucocorticoids) have been associated with mechanisms of preterm delivery and fetal brain injury leading to cognitive impairments.

The neurodevelopmental side effects might be caused by neonatal illness such as bronchopulmonary dysplasia and chronic lung disease that can lead to brain injury because of the poor oxygen delivery to the brain cells. Also, there are suggestions that poor postnatal nutrition and steroid-medication therapy may lead to brain injury. Neuroimaging findings include periventricular leukomalacia, intraparenchymal hemorrhage, intraventricular hemorrhage, porencephaly, hydrocephalus, and other white matter signs of injury.

There are some evidences that mental health of a mother can influence the neurological outcomes for children who are born preterm. It is often seen that mothers of prematurely born infants experience more depression which affects their parenting abilities. This mental distress has long-term effects on children and their cognitive development.

It should be noted, however, that all observations mentioned above are statistical: this means that plenty of preterm babies build successful careers and achieve great things in life. It’s enough t mention that such famous scientists as Isaac Newton, Albert Einstein and Charles Darwin were born prematurely.

References

Basten, M., Jaekel, J., Johnson, S., Gilmore, C., & Wolke, D. (2015). Preterm Birth and Adult Wealth: Mathematics Skills Count Psychological Science DOI: 10.1177/0956797615596230

Cooke, R. (2005). Are there critical periods for brain growth in children born preterm? Archives of Disease in Childhood – Fetal and Neonatal Edition, 91 (1) DOI: 10.1136/adc.2005.077438

Goldenberg RL, Culhane JF, & Johnson DC (2005). Maternal infection and adverse fetal and neonatal outcomes. Clinics in perinatology, 32 (3), 523-59 PMID: 16085019

Lefebvre F, Mazurier E, & Tessier R (2005). Cognitive and educational outcomes in early adulthood for infants weighing 1000 grams or less at birth. Acta paediatrica (Oslo, Norway : 1992), 94 (6), 733-40 PMID: 16188777

Saugstad OD (2005). Oxygen for newborns: how much is too much? Journal of perinatology : official journal of the California Perinatal Association, 25 Suppl 2 PMID: 15861173

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