PHILADELPHIA (CBS) – A new study conducted by the Children’s Hospital of Philadelphia reveals that oftentimes, healthy babies are being delivered too early.

The research looked at millions of U.S. births over 15 years and found that about three to four percent of babies were delivered early for no medical reason. While that might not seem like a big number, the study’s authors say each percentage point represents 40,000 babies.

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Furthermore, the rate of nonindicated births before 39 weeks was 86% higher in 2009 than in 1995.

Older maternal age, higher income levels, delivering at smaller-volume or non-teaching hospitals and private health insurance all increased the odds of an early c-section or induction. Non-Hispanic black women were more likely than non-Hispanic white women to have a nonindicated early-term c-section but less likely to undergo nonindicated labor induction.

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The research, which is published in the July issue of Medical Care, also found that babies born early – either by c-section or induction – were more likely to have a longer hospital stay.

Early term birth by c-section is also associated with a higher risk of respiratory problems.

“A growing body of research suggests that health outcomes are worse for infants born before 40 weeks gestation, compared to full-term births,” said Scott A. Lorch, M.D., M.S.C.E., a neonatologist at The Children’s Hospital of Philadelphia (CHOP). “Unfortunately, many of these earlier births are ‘nonindicated,’ meaning there is not a medical rationale to deliver the baby early. We analyzed the extent to which these infants are born too soon and without medical indication.”

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To see the study, click here.