Of the women who attempted a vaginal birth after cesarean delivery, only 0.7 percent, or 124 women in all, experienced a rupture of the uterus. The study also found that using drugs to induce or speed up labor may also increase the chances for uterine rupture. Such drugs increase the force and duration of uterine contractions. Of the 1864 women given the drug oxytocin alone, without any other drugs to induce labor, 1.1 percent (20 women) had a uterine rupture. None of the 227 women receiving the drugs known as prostaglandins alone experienced uterine rupture. Dr. Spong explained, however, that it's possible that the study sample did not include a sufficient number of women to determine a small increase in uterine rupture from prostaglandins alone.
Among the infants born to the women who attempted vaginal birth after a Cesarean, .08 percent (12) were diagnosed with hypoxic ischemic encephalopathy, a condition that may result from lack of oxygen to the baby's brain. The lack of oxygen may be caused by heavy maternal bleeding, detachment of the placenta, or other complications. Of these 12, seven were associated with a uterine rupture, and two of the babies died. In contrast, none of the infants whose mothers had an elective cesarean delivery developed hypoxic ischemic encephalopathy.
Among the women who attempted vaginal birth, the overall risk for either brain injury to the baby or death to the baby at term from uterine rupture was roughly 1 in 2000 trials of labor, said Mark B. Landon, M.D., of Ohio State University and the lead investigator for the NICHD Maternal-Fetal Medicine Units Network Cesarean Registry.
Women who attempted vaginal birth after cesarean were also more likely to develop infection of the uterine lining (2.9 percent) as compared to women who had an elective repeat Cesarean delivery (1.8 percent). The study authors found no significant difference between the percentage of women who required a hysterectomy: 0.2 percent in the labor group and 0.3 percent in the C-section group. Similarly, there was no significant difference in the maternal death rate between the two groups of women (.02 percent versus .04 percent.)
Dr. Spong said that the only way to arrive at a more accurate estimate of the risks involved would be to assign women at random to either a vaginal delivery or to have a repeat C-section. It's possible, she added, that the women who chose labor may differ in some unknown way from the women who had repeat Cesarean delivery, and that this difference might have influenced the study's results.
Still, Dr. Spong said, because of the large number of women who took part in study, and the careful, systematic way the researchers collected the data, the current study offers the most reliable estimate to date of the risks conveyed by attempting vaginal delivery after a prior Cesarean delivery.
The NICHD is part of the National Institutes of Health (NIH), the biomedical research arm of the federal government. NIH is an agency of the U.S. Department of Health and Human Services. The NICHD sponsors research on development, before and after birth; maternal, child, and family health; reproductive biology and population issues; and medical rehabilitation. NICHD publications, as well as information about the Institute, are available from the NICHD Web site, http://www.nichd.nih.gov, or from the NICHD Information Resource Center, 1-800-370-2943; e-mail NICHDInformationResourceCenter@mail.nih.gov.
