Summary of New Study Links Premature Birth to Worse School Grades:
This study examined the IQ scores of military conscription intelligence tests to evaluate the cognitive function of individuals born before 34 weeks gestation. The results showed a significantly lower score in math and language tests during adolescence, as well as a reduction in IQ points for those born before 34 weeks. The researchers suggest that cognitive outcomes are heavily influenced by social circumstances and early intervention is warranted for children born preterm. They also note that the causes of preterm birth are complex and socio-environmental factors should be improved to mitigate any associated neurocognitive deficits.
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Premature Birth Linked to Lower IQ Scores and Math and Language Test Results
A recent large population study published in The BMJ has revealed that premature birth, before 34 weeks of pregnancy, is associated with lower scores in math and language tests during adolescence in comparison to those born at full term (40 weeks).
It is estimated that around 15 million infants are born preterm, before 37 weeks of pregnancy, worldwide each year. The final weeks of pregnancy are significant for fetal brain development, and preterm and early-term birth are thought to have a negative impact on later brain function.
The Study
To more accurately determine the impact of gestational age—duration of pregnancy in weeks—at birth on long-term cognitive function, the researchers analyzed data for all full siblings born in Denmark from 1 January 1986 to 31 December 2003.
A total of 1.2 million children were born in this period, of whom 792,724 had at least one full sibling born in the same period, which allowed the researchers to take into account hereditary factors such as maternal intelligence.
Using nationwide registry information, the researchers analyzed gestational age at birth, along with their exam results in written Danish language and maths at age 15-16, and separately, the results of intelligence tests taken by 227,403 brothers aged around 18, at mandatory military conscription.
Potentially influential factors, including sex, birth weight, parental age and educational level at birth, number of older siblings, and shared family factors between siblings were also taken into account in the analysis.
The Results
Overall, 44,322 (5.6%) of the 792,724 children were born before 37 weeks. Of these, only those born before 34 weeks had significantly lower than average maths scores than those born at 40 weeks, and grades progressively decreased with increasing prematurity.
For written language, however, only children born at or less than 27 weeks showed a significantly lower-than-average grade.
Analysis of military conscription intelligence test scores, measured in IQ points, also showed markedly lower test scores for those born before 34 weeks. For those born after 34 weeks, there was a less than 1 point reduction in IQ, compared with those born at 40 weeks. But there was a 2.4 point IQ reduction for those born between 32-33 weeks, a 3.8 point reduction for 28-31 weeks, and a 4.2 point reduction for those born at or before 27 weeks.
The Implications
This is an observational study so can’t establish cause and the researchers also acknowledge some limitations. For instance, smoking during pregnancy was not recorded before 1991, and test results may differ from real-life outcomes such as lifetime income.
But they say the study has the advantage of a large sample size and their sibling comparison design most likely accounts for other factors such as maternal smoking. Results were also similar after further analyses, such as including children who did not take exams, suggesting that the findings withstand scrutiny.
While the underlying reasons
