Morse and his colleagues evaluated Florida birth records between 1996 and 1997, and identified nearly 160,000 singleton infants born between 34 and 42 weeks to include in their analysis. Most of the children -- 152,661 -- were born between 37 and 42 weeks' gestation, which is considered full-term. Slightly more than 7,000 were born between 34 and 36 weeks. The researchers then compared birth information with pre-school and kindergarten school records.
They found that the risk of a developmental delay or disability was 36 percent higher for the babies born between 34 and 36 weeks. A developmental delay or disability may include physical, language, cognitive and socio-emotional development, according to the researchers.
The study also found that children who were born late pre-term had a 19 percent higher risk of being suspended in kindergarten. The risk of having to stay back in kindergarten was increased 11 percent for the children born early.
Morse said the researchers tried to control the data for the many factors that can influence a child's life between birth and school-age. They compensated for factors such as maternal age, education, socioeconomic states, maternal alcohol use and more.
He said the researchers think there's simply a lot of brain maturation that goes on during those last four weeks, and babies who are born early may be missing out on some of that growth process.
"This study shows that a late pre-term baby is not the same as a term baby," said Morse.
Kloesz added: "If you look at the risk for any one specific child, it's not terrible. But, if you look at all of these children, it's a huge societal risk."
Learn what steps you can take to help prevent premature birth from the March of Dimes.
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