London: Children born either too early or too late may have lower school grades at the age of 16, say scientists who found that gestational period may have a long-term effect on academic performance, a new study has found.
The risk of cognitive and developmental problems in premature infants is well-established, but preventing preterm birth is limited clinically. By contrast, less is known about what happens to cognitive performance in children born post-term, or about the influence of birth weight variations within post-term populations, where there may be more scope for intervention.
The study details the relationship between gestational age at birth and school grades at age 16 across the full range of pregnancy duration (22 to 45 completed weeks), by weight-for-gestational age, focusing on extremely pre- and post-term births and taking account of possible effects within and between families. Gestation is the period of time between conception and birth. During this time, the baby grows and develops inside the mother's womb.
Using the whole Swedish population, over 2 million live births between 1973 and 1994 were linked to the Sweden National School Register and other registers from Statistics Sweden and the National Board of Health and Welfare. Academic performance was measured by the final grade achieved on completing secondary education at 16. Between 1973 and 1994, 9.4 per cent of Swedish births were post-term and 4.6 per cent preterm.
Late preterm children (3.6 per cent) were more likely to have been exposed to maternal medical risk or birth complications. Grade averages were lower for pre- and post-term children than for term-counterparts, and were lowest in children showing evidence of poor foetal growth, irrespective of gestational age.
Grades of pre- and post-term children remained lower than those of term counterparts when considering spontaneous deliveries, uncomplicated unassisted deliveries, children with normal Apgar, or without congenital anomalies. However, induced post-term deliveries were not associated with reduced school performance.
Among matched siblings, within-family effects were weaker, particularly in the preterm sibling cohort and less so in post-term children. This attenuation of effect suggests confounding by unmeasured familial traits. Residual within-family associations suggested there may also be direct causal links between birth at early or late GA and school-leaving age academic performance.
"Less favourable outcomes of post-term infants with poor foetal growth suggest that placental insufficiency may become particularly toxic to neurodevelopment the longer a pregnancy endures," said lead author Hein Heuvelman. The study was published in the International Journal of Epidemiology.
