Risk factors for complete uterine rupture.

BACKGROUND: Complete uterine rupture is a rare peripartum complication associated with a catastrophic outcome. Because of its rarity, knowledge about its risk factors is not very accurate. Most previous studies were small and over a limited time interval. Moreover, international diagnostic coding was used in most studies. These codes are not able to differentiate between the catastrophic complete type and less catastrophic partial type. Complete uterine rupture is expected to increase as the rate of cesarean delivery increases. Thus, we need more accurate knowledge about the risk factors for this complication.

OBJECTIVE: The objective of the study was to estimate the incidence and risk factors for complete uterine rupture during childbirth in Norway.

STUDY DESIGN: This population-based study included women that gave birth after starting labor in 1967-2008. Data were from the Medical Birth Registry of Norway and Patient Administration System, complemented with information from medical records. We included 1,317,967 women without previous cesarean delivery and 57,859 with previous cesarean delivery. The outcome was complete uterine rupture (tearing of all uterine wall layers, including serosa and membranes). Risk factors were parameters related to demographics, pregnancy, and labor. Odds ratios for complete uterine rupture were computed with crude logistic regressions for each risk factor. Separate multivariable logistic regressions were performed to calculate the adjusted odds ratios and 95% confidence intervals.

RESULTS: Complete uterine rupture occurred in 51 cases without previous cesarean delivery (0.38 per 10,000) and 122 with previous cesarean delivery (21.1 per 10,000). The strongest risk factor was sequential labor induction with prostaglandins and oxytocin, compared with spontaneous labor, in those without previous cesarean delivery (adjusted odds ratio, 48.0, 95% confidence interval, 20.5-112.3) and those with previous cesarean delivery (adjusted odds ratio, 16.1, 95% confidence interval, 8.6-29.9). Other significant risk factors for those without and with previous cesarean delivery, respectively, included labor augmentation with oxytocin (adjusted odds ratio, 22.5, 95% confidence interval, 10.9-41.2; adjusted odds ratio, 4.4, 95% confidence interval, 2.9-6.6), antepartum fetal death (adjusted odds ratio, 15.0, 95% confidence interval, 6.2-36.6; adjusted odds ratio, 4.0, 95% confidence interval, 1.1-14.2), and previous first-trimester miscarriages (adjusted odds ratio, 9.6, 95% confidence interval, 5.7-17.4; adjusted odds ratio, 5.00, 95% confidence interval, 3.4-7.3). After a previous cesarean delivery, the risk of rupture was increased by an interdelivery interval <16 months (adjusted odds ratio, 2.3; 95% confidence interval, 1.1-5.4) and a previous cesarean delivery with severe postpartum hemorrhage (adjusted odds ratio, 5.6; 95% confidence interval, 2.4-13.2).

CONCLUSION: Sequential labor induction with prostaglandins and oxytocin and augmentation of labor with oxytocin are important risk factors for complete uterine rupture in intact and scarred uteri.