Predicting Cesarean Section and Uterine Rupture among Women Attempting Vaginal Birth after Prior Cesarean Section

Background: There is currently no validated method for antepartum prediction of the risk of failed vaginal birth after cesarean section and no information on the relationship between the risk of emergency cesarean delivery and the risk of uterine rupture. Methods and Findings: We linked a national maternity hospital discharge database and a national registry of perinatal deaths. We studied 23,286 women with one prior cesarean delivery who attempted vaginal birth at or after 40-wk gestation. The population was randomly split into model development and validation groups. The factors associated with emergency cesarean section were maternal age (adjusted odds ratio [OR] = 1.22 per 5-y increase, 95% confidence interval [CI]: 1.16 to 1.28), maternal height (adjusted OR = 0.75 per 5-cm increase, 95% CI: 0.73 to 0.78), male fetus (adjusted OR = 1.18, 95% CI: 1.08 to 1.29), no previous vaginal birth (adjusted OR = 5.08, 95% CI: 4.52 to 5.72), prostaglandin induction of labor (adjusted OR = 1.42, 95% CI: 1.26 to 1.60), and birth at 41-wk (adjusted OR = 1.30, 95% CI: 1.18 to 1.42) or 42-wk (adjusted OR = 1.38, 95% CI: 1.17 to 1.62) gestation compared with 40-wk. In the validation group, 36% of the women had a low predicted risk of caesarean section ( 40%); 10.9% and 47.7% of these women, respectively, actually had deliveries by caesarean section. The predicted risk of caesarean section was also associated with the risk of all uterine rupture (OR for a 5% increase in predicted risk = 1.22, 95% CI: 1.14 to 1.31) and uterine rupture associated with perinatal death (OR for a 5% increase in predicted risk = 1.32, 95% CI: 1.02 to 1.73). The observed incidence of uterine rupture was 2.0 per 1,000 among women at low risk of cesarean section and 9.1 per 1,000 among those at high risk (relative risk = 4.5, 95% CI: 2.6 to 8.1). We present the model in a simple-to-use format. Conclusions: We present, to our knowledge, the first validated model for antepartum prediction of the risk of failed vaginal birth after prior cesarean section. Women at increased risk of emergency caesarean section are also at increased risk of uterine rupture, including catastrophic rupture leading to perinatal death. By studying a large group of Scottish women giving birth, Gordon Smith and colleagues developed and validated a tool to assess the risk of failed vaginal birth after prior caesarean section. Background: The number of cesarean sections performed is increasing. Many women who have had a previous cesarean section want to try to have a vaginal birth in the next pregnancy, but they and their doctors may be worried about whether or not it is safe for them and the baby to attempt the vaginal birth. What Did the Researchers Do and Find?: They looked at a large number of women in Scotland who had had one previous cesarean section and who were about to have another baby. Altogether they studied 23,286 women who had attempted to give birth vaginally between 1985 and 2001. They split the women into two groups; using one group, they developed a way of predicting the outcome (whether or not the women were going to need an emergency cesarean section) by looking at various risk factors including mother's age, height, sex of baby, gestation, and whether and how the birth was induced. Then, using the second group of women, they tested the model they had developed. They discovered that they could identify half of the women as being at high or low risk of needing emergency cesarean section, with the remainder being at intermediate risk. The things that increased risk were older maternal age, smaller height, male sex of baby, labor induced by prostaglandin, not having had a previous vaginal birth, and later birth. They also found that the risk of having a ruptured uterus went up as the risk of emergency cesarean section went up. What Do These Findings Mean?: Obstetricians will be able to use the model developed to try to give women a more accurate estimate of whether they will need to have a cesarean section once they have had one in a previous pregnancy. Where Can I Get More Information Online?: The following Web sites have relevant information.