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"Women having their first baby who have a long cervix around 23 weeks of pregnancy are more likely to be delivered by emergency Caesarean section during labor at term," the study's lead author, Dr. Gordon Smith, head of obstetrics and gynecology at Cambridge University in the United Kingdom, said in a prepared statement.
"The nature of this finding is not such that women should now have this measurement performed to predict Caesarean section risk," he added. "The key issue in this analysis is understanding the processes that lead to normal and abnormal labor."
Several experts said that doctors won't be measuring your cervix halfway through your pregnancy to predict whether or not you'll have a natural birth any time soon.
"If the cervix hasn't prepped itself for labor, there's something going on," said Dr. Miriam Greene, an obstetrician at New York University Medical Center. "The idea that a longer cervix leads to a greater risk of Caesarean makes sense. The question is, if I start checking at 23 weeks and find a longer cervix, what then?"
Dr. Robert Lorenz, director of maternal-fetal medicine at Beaumont Hospital in Royal Oak, Mich., echoed Greene's sentiment. "This is a very interesting study that gives us another perspective on what happens in labor, but I don't think it has any immediate clinical applications," he said. Even years from now, he added, he's not sure anyone would intervene at 23 weeks, because "anything you do to change the cervix at 23 weeks might bring on preterm birth."
But both Greene and Lorenz said the new study was impressive because of the large numbers of women included, and because it adds to scientists' understanding of what happens to a woman's body during pregnancy and delivery.
The study, published in the March 27 issue of the New England Journal of Medicine, included almost 25,000 women who had their cervical length measured at 23 weeks of gestation using transvaginal ultrasound.
Caesarean rates were highest among those women with the longest cervix measurements. The women whose cervical measurements were between 40 and 67 millimeters long had a 25.7 percent C-section rate, compared to a 16 percent rate in those with the shortest cervical measurements — 16 to 30 millimeters. C-section rates were 18 percent and 22 percent for the third and fourth quartile cervix measurements, respectively.
That translates to an 80 percent increased chance of a Caesarean section for a woman with the longest cervical measurements, according to the study.
"Studies in a number of species have suggested that the uterus prepares for labor well in advance of term. However, this is the first major study to suggest that the same is true in women," Smith said.
SOURCES: Gordon C.S. Smith, M.D., Ph.D., head, obstetrics and gynecology, Cambridge University, United Kingdom; Robert Lorenz, M.D., director, maternal-fetal medicine, Beaumont Hospital, Royal Oak, Mich.; Miriam Greene, M.D., obstetrician and gynecologist, New York University Medical Center, and clinical assistant professor, New York University School of Medicine, New York City, and co-author of Frankly Pregnant: A Candid, Week-by-Week Guide to the Unexpected Joys, Raging Hormones and Common Experiences of Pregnancy; March 27, 2008, New England Journal of Medicine
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