When mothers deliver later, babies are more likely to have physical problems, but they also are likely to have cognitive benefits down the road, suggests provocative new Northwestern University research published Monday in JAMA Pediatrics.
It is well known that continuing a pregnancy beyond 40 weeks can increase the risk of physical disabilities for the child, but this is the first study to document cognitive benefits, as well as physical risks, for late-term infants.
“Our hope is that this research will enrich conversations between ob-gyns and expectant parents about the ideal time to have the baby,” said Dr. David Figlio, economist, lead author of the JAMA study and director of the Northwestern Institute for Policy Research.
In the JAMA study, late-term infants, compared to full term, had higher average test scores in elementary and middle school; a 2.8 percent higher probability of being gifted; and a 3.1 percent reduced probability of poor cognitive.
The late-term infants, however, also had a 2.1 percent higher rate of physical disabilities at school age and higher rates of abnormal conditions at birth.
“The tradeoff between cognitive and physical outcomes associated with late term births is something parents and physicians should discuss,” said Mr. Figlio, also the Orrington Lunt Professor of Education and Social Policy at the Northwestern School of Education and Social Policy.
The researchers used a unique data set — matched birth and education records for more than 1.4 million Florida school children – to find that late-term (41 weeks) children did better in school in the long run, but also had a higher risk of physical disability than their full term counterparts (39 or 40 weeks).
The research builds on a previous study by Mr. Figlio’s team using the same Florida data set that found that heavier newborns have an academic edge.
“Armed with the information we learned from the work on birth weight and cognitive outcomes, we began thinking about the single best way to pack on more birth weight which means keeping the baby in utero longer,” Mr. Figlio said. “We wanted to know: Is there a cost associated with delivering these babies?”