The increasing number of preterm births in the U.S. during the early 1990s and 2000s appear linked to the increasing number of medically induced labors, according to a new study.

The number of preterm births across the U.S. rose by 30 percent between 1992 and 2004, and that increase may be attributable to the number of medically induced labors, which nearly doubled during the same period, researchers found.

Doctors induce labor in women for various reasons, including medical problems with the baby or a woman being past due for delivery. Some doctors, however, may be inducing labor around the 34th week of pregnancy, which is considered preterm even though it is near the end of a typical 37- to 39-week gestation.

Past studies have shown that being preterm - even late preterm - increases a baby’s risk for complications soon after delivery, such as needing to be put on a respirator, as well as for problems later in life.

So the fear is that the rising number of preterm babies increases the number at risk for these complications.

The study’s senior researcher said he doesn’t think doctors are inducing labor for non-medical reasons; they may just be erring on the side of caution by delivering the babies early for good medical reasons.

The problem, said Dr. Michael Kramer, is that the decision to do early labor induction is “socially contagious.”

“I think the threshold has been going down for induction over the years, and I don’t think we’ve shown that’s been a benefit,” said Kramer, of the McGill University Faculty of Medicine in Montreal.

To see whether increased rates of labor induction were linked to the rise in preterm births, Kramer and his colleague used data from the U.S. National Center for Health Statistics to compare the labor induction and preterm birth rates in each state for non-Hispanic white women between 1992 to 1994 and 2002 to 2004.

Overall, preterm births increased by nearly a third over those 13 years, from 6.4 percent in 1992 to 8.5 percent in 2004. During that time, labor inductions rose from 13.7 percent in 1992 to 26 percent.

The researchers, who published their study in BJOG: An International Journal of Obstetrics & Gynaecology, also examined whether C-sections were linked to the rise in preterm births.

While there was a rise in C-sections throughout the U.S. during the study period, the researchers say that is not a major factor contributing to preterm births because most C-sections are done during naturally-occurring labors - not during early inductions of labor.

Kramer told Reuters Health that he believes doctors can curb the rise in preterm births without conferring additional risk on the babies. That goal is already being realized in Ohio.

Through an elective education program known as the Ohio Perinatal Quality Collaborative, more women appear to be delivering their babies near full term (39 to 41 weeks) instead of “near term” (36 to 38 weeks) since the initiative started in 2008.

“It’s tremendously successful and thousands of women in Ohio have moved to late-term delivery from pre-term delivery,” said Dr. Michele Walsh, a member of OPQC and chief of neonatology at UH Rainbow Babies & Children’s Hospital in Cleveland.

For women in other states, Kramer told Reuters Health that women should be involved in their medical decisions and understand labor induction carries some risk.

SOURCE: BJOG: An International Journal of Obstetrics & Gynaecology, online August 13, 2012.

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