In the new study, researchers working with the Consortium on Safe Labor collected data on cesarean delivery throughout the United States using data from almost 229,000 electronic medical records from 19 hospitals.
They found that 30.5 percent of all deliveries were done by cesarean section in 2007, including 31.2 percent of women having their first child.
Among women who underwent C-section due to an abnormal or difficult childbirth or labor (dystocia), half of the deliveries were done before the cervix had opened less than 6 centimeters -- early in the labor process, Zhang said.
Among women who had a cesarean delivery before going into labor, about 31 percent had a uterine scar from an earlier pregnancy. A uterine scar can be caused by many conditions that damage the uterus. In some cases, scar tissue can prevent the uterus from fully dilating, thus resulting in a C-section.
However, almost 29 percent of women with a uterine scar did manage to have a normal vaginal delivery, the researchers noted. And in these cases, vaginal delivery was successful in about 6 out of 10 cases.
There are many reasons that could help explain why the number of cesarean deliveries is rising, the researchers said. These include women delaying childbirth until they are approaching middle-age, increasing obesity rates among pregnant women and the increase in multiple births due to the use of fertility treatments.
Also, when a woman has already had one C-section, doctors are likely to deliver her other children the same way. That's a practice obstetrical experts have been trying to curb, however. In July, the American College of Obstetricians and Gynecologists issued new guidelines stressing that many women who've had a C-secti
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