Children born on the shorter end of that range scored lower on math and reading tests as 8-year-olds than those born later, researchers wrote in the journal Pediatrics, but they added that the differences were small.

"Certainly the vast majority of 37-weekers and 41-weekers would end up developing typically," said Kimberly Noble, the lead author on the study from Columbia University Medical Center and New York-Presbyterian Hospital.

Still, until more research is done, she said, "we would urge caution to both parents and physicians when considering early elective delivery."

Noble and her colleagues compared birth records and third-grade standardized test scores for 128,000 children born in New York City in the late 1980s and early 1990s who went to citywide public schools. All of them had been born between 37 and 41 weeks' gestation.

On both reading and math exams, where a score of 50 was considered average, kids born at 41 weeks scored about one point higher, in general, than those born at 37 weeks.

That's equivalent to about a 1.5 point difference on an IQ test, Noble said.

"That would not be a difference that would likely be noticeable from one child to the next," she told Reuters Health. "Where it is more noticeable is on the lower end of the (test score) distribution."

For example, children born at 37 weeks were 23 percent more likely to have at least moderate reading impairment, and 19 percent more likely to have moderate math impairment, than those born on the late end of the term range.

Noble said the finding doesn't prove that being born early-term can slow kids' brain development and hurt their academic achievement, since it's possible that other factors are related both to early births and academic difficulties.

Marie McCormick, a maternal and child health researcher from the Harvard School of Public Health in Boston, agreed that was one limitation of the study.

"Even if it's an early term delivery, there may have been something going on that led to that child being born earlier in the process than later," she said.

Still, the findings are consistent with some previous research suggesting that babies born at 37 or 38 weeks may be different from those born slightly later, she added.

The researchers agreed that although the findings shouldn't be too concerning, they are something to consider for women who have some control over when their babies will be born, such as those scheduling a cesarean section.

"The main thing is ... when you're coming to the discussion about delivery and if you have a decision about the timing of that delivery, to really make sure that you're as far along in pregnancy as you can get without getting out of the range of normal," McCormick said. SOURCE: bit.ly/jsoh2P

(Reporting from New York by Genevra Pittman at Reuters Health; editing by Elaine Lies and Bob Tourtellotte)

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