The brain of a baby at 34 weeks' gestation weighs 35 percent less than it would at term, the study noted.
Social factors and gender had the greatest impact on the children's mental scores, the study said, with language spoken at home playing a key role. (Boys were most likely to have severe development delays.) In contrast, gestational age was the most important contributor to physical delays.
Researchers noted a few study limitations, including the lack of information on possible newborn medical complications and the possible weaknesses of infant developmental testing.
However, their findings are consistent with those of other recent studies of late preterm infants, they said. Researchers have found such infants are at higher risk for respiratory problems, worse academic performance and school suspension down the road.
"There's a reason why normal gestation is 40 weeks," said Dr. Marty Ellington Jr., chairman of the department of pediatrics at Lenox Hill Hospital in New York City. "If a child needs to be delivered for a maternal or infant medical condition, care has advanced where those children can do quite well. But we should never discount the importance of those two to four weeks. If we have a choice, we would want the child to go to term."
Woythaler said more research is needed to determine how to best help preterm babies suffering developmental delays reach the same level as their peers carried to term.
"Very premature infants automatically get referred to early intervention," she said. "Not these infants. Not all of these infants are doing poorly -- a lot are doing well and normally. Once we can pinpoint which infants can benefit from early intervention, that's the point we can do something."
Ellington pointed out that gender and medical issues t
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