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More and More Babies Born Too Soon

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Dramatic Increase in Preterm Births continued...

"Assisted reproduction, as it has been practiced, carries a high risk of multiple births. With multiple births you can be absolutely certain of having more preterm deliveries," says epidemiologist David A. Savitz, PhD. "Studies have suggested that at least a third of the total increase in preterm births can be attributed to multiple gestations."

Thanks to advances in diagnostic testing, obstetricians are also better able to monitor fetal and maternal distress than they have been in the past. As a result, inducing labor between 35 and 37 weeks gestation is far more common than it once was. The practice is somewhat controversial, and some argue that is being done too often.

"The willingness of clinicians to deliver early is probably greater now than it has ever been," Savitz says. "I don't think they perceive any problem whatsoever at delivering a baby at 35 or 36 weeks. But when you look at large population studies, these babies do have a slightly increased risk of [death] and certain developmental problems."

Charles J. Lockwood, MD, who leads the American College of Obstetricians and Gynecologists' committee on obstetrical practice, has a different view. Induction prior to 37 weeks is virtually never done without good reason, he says.

"Early inductions have certainly increased, but the reasons behind them more than justify the reasons for doing them," Lockwood tells WebMD. "Fetuses in distress are more likely to die and have long-term problems, so there are very good reasons for delivering them between 35 and 37 weeks."

Early Delivery: 'A Problem We Should Have Solved'

While the rise in preterm deliveries may be explainable, doctors have had less success preventing naturally occurring early births. It is widely believed that stress and infections play a major role -- accounting for roughly 70% of premature deliveries, Lockwood says -- but ob-gyns have not yet figured out how to treat these labor triggers. Trials using antibiotics to treat infections in pregnant women have so far been disappointing.

"With all of our new toys and equipment, and with all of our new leaps in gene research, we still don't know how to keep women from delivering early," says epidemiologist Claudia Holzman, PhD, of Michigan State University. "The big story isn't that preterm deliveries are on the increase, it is that we haven't solved the problems that cause them."

"The fact is, this is a problem we should have solved, but we are still grappling with it," echoes the March of Dimes' Mattison.

Holzman and MSU colleagues are evaluating sources of stress and responses to it in a group of 1,500 women being followed from midpregnancy. The researchers are studying stress-related responses such as blood pressure, heart rate, and hormone levels.

Hormones released in response to stress may make blood vessels narrow, causing damage to the placenta and prompting premature delivery. Stress responses may also damage the immune system, promoting uterine infections implicated in premature delivery. And stress is believed to boost production of a hormone -- called corticotropin-releasing hormone -- that is thought to play a role in triggering labor.

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