Long term effects of prematurity: A glass half full of girls.

By Nestor Lopez-Duran PhD

Back in June I commented on an article that examined the mechanisms behind the type of cognitive disabilities experienced by very preterm children. That study showed marked impairment among premature kids, which is consistent with a long line of research showing significantly increased risks for cognitive deficits among children born under 30-week gestation. However, most of these studies were conducted decades ago, before significant advances in treatment and intervention programs for premature infant. Thus this begs the question, do children born extremely premature in the 1990s and 2000s continue to show significant levels of cognitive impairment?

In the latest issue of Pediatrics, a British team of researchers presented a cohort study of 219 survivors of extreme prematurity. The authors examined the cognitive and clinical profile of these kids at age 6 and 11, and compared them to  a group of 153 typically developing peers. The children completed a series of neurocognitive tasks, including the Kaufman-Assessment Battery for Children, a full pediatric evaluation to assess for the presence of cerebral palsy, motor functioning, and sensory impairment.

The results:

  1. Mean composite cognitive functioning scores were significantly lower in the preterm kids compared to their peers  (score of 83.7  vs. 104.1). This effect did not appear to be explained by socio-economic status of the families.
  2. Among typically developing peers, there was no difference in cognitive functioning between boys and girls. However, among the preterm children, boys had significantly lower cognitive scores than girls (by 8 points).
  3. When categorizing the impairment into 4 levels (severe, moderate, mild, no impairment), serious impairment (severe or moderate) was observed in 40% of preterm kids but only 1.3% of their typically developing peers. A gender effect was also observed. Serious impairment was seen in 50% of preterm boys but only 31% of preterm girls.
  4. Cerebral palsy was also twice as common among boys (25%) than girls (11%).
  5. Finally, as you can see in the graphic below, the rates of disabilities from age 6 to 11 did not change much. However, there appears to be a slight decrease in the rate of severe disability with a comparable increase in the rate of moderate disability.

Rates of disability among preterm children

In sum, the rates of serious cognitive deficits among preterm children are around 50%, indicating that despite advances in care, prematurity continues to lead to significant cognitive impairment. However, the rates of impairment among girls were significantly lower than among boys. Although it seems surprising that boys were more susceptible to the effects of prematurity than girls, other studies have reported similar findings. In fact, premature boys have lower survival rates than girls, suggesting that differences in the sex differentiation process before birth (such as exposure to androgens) may place boys at higher risk. Are there any neonatal endocrinologists in house who could shed some light on why exposure to androgens before birth may lead to greater susceptibility to developmental insults?

The reference:

Johnson, S., Fawke, J., Hennessy, E., Rowell, V., Thomas, S., Wolke, D., & Marlow, N. (2009). Neurodevelopmental Disability Through 11 Years of Age in Children Born Before 26 Weeks of Gestation PEDIATRICS, 124 (2) DOI: 10.1542/peds.2008-3743