Uterine rupture, a rare but catastrophic obstetric emergency, is defined as a complete or full- thickness disruption of all the uterine layers including the serosa; it may occur in an unscarred or scarred uterus. The commonest scar encountered is that of previous cesarean section (CS). Premonitory signs like maternal tachycardia, abnormal CTG, severe abdominal pain, scar tenderness, vaginal bleeding, hematuria, loss of station of presenting part and should clue the clinician to impending rupture. Rupture is associated with serious maternal hemorrhage, fetal distress or demise, and urgent laparotomy, all of which contribute to high maternal and perinatal morbidity and mortality. On the other hand, uterine dehiscence is an incomplete disruption of a preexisting uterine scar with intact uterine serosa. Dehiscence is more common than rupture, is often occult and outcomes are better as hemorrhage is less and the fetus, umbilical cord and placenta are contained within the uterus.
It bears remembering that though previous uterine scar is an important factor for rupture, majority of cases with scarred uteri result in dehiscence rather than rupture. In developed countries, uterine rupture is usually seen with trial of labor after previous lower segment cesarean section (LSCS). A WHO systematic review published in 2005 on the worldwide prevalence of uterine rupture and subsequent maternal morbidity and mortality found that in developed countries, prevalence of rupture with previous CS was around 1%, and in women without previous CS, prevalence was extremely rare, <1 per 10,000. Rising primary cesarean section rates, and in response to this trend, rising rates of trial of labor after cesarean (TOLAC) are responsible for rupture; WHO recommends that efforts should focus on reduction in CS rates and careful monitoring of patients who opt for vaginal birth after CS (VBAC).
The scenario of uterine rupture is quite different in resource- poor settings, where the WHO review found that in least- developed countries (Nigeria, Ghana, Bangladesh), 75 % of cases of rupture were seen in unscarred uteri, with attendant high maternal mortality (1 to 13 %) and perinatal mortality (74 to 92 %). Studies from the Indian subcontinent have shown that prolonged obstructed labor and lack of access to operative delivery are still the main cause of uterine rupture, followed by scarred uterus. A ten year analysis of uterine rupture by Sahu from a teaching hospital (JIPMER Pondicherry) found majority (70%) in unbooked cases, with an equal distribution of rupture among scarred and unscarred uteri. In patients with unscarred uterus, cephalopelvic disproportion (CPD) followed by malpresentation was the leading cause. Postpartum hemorrhage was seen in 66% of cases and as many as 83% cases required blood transfusion. They reported a perinatal mortality of 94.07% and maternal mortality of 2.76%. These figures are probably representative of data from major referral centers in the country; they put a huge burden on existing healthcare facilities.
Risk factors for uterine rupture are well known and include number and type of previous CS: one previous LSCS (further classified as single or two-layer closure), one previous low vertical incision, previous classical CS or multiple previous CS; the risk of scar rupture increases to approximately 2% with 2 or more previous CS. Other uterine surgeries like myomectomy, congenital anomalies of the uterus, labor induction especially with prostaglandins, dystocia, CPD, instrumentation and trauma are also important risk factors. Conversely, longer inter-pregnancy interval after previous CS (> 2 years) allows the scar to recover its maximum tensile strength and reduces the risk of rupture. Previous successful vaginal birth especially previous VBAC, is the single most important predictor of successful vaginal delivery.
Women with previous CS opting for VBAC versus elective repeat CS should be counseled in the antenatal period and a clear defined labor plan in accordance with current guidelines should be documented. VBAC should be considered in optimum clinical settings with facilities for close monitoring and resources for immediate LSCS and neonatal resuscitation. Patients should be informed about the high chance (>70 %) of successful VBAC after one previous LSCS and the low risk of rupture uterus (22 – 74/ 10,000). However they should also be informed that induced labor, especially with prostaglandins, carries a higher risk of uterine rupture.
A Cochrane review in 2013 on VBAC has met with some criticism as their conclusions are not precise. They state that “planned elective repeat cesarean section and planned VBAC for women with prior cesarean birth are both associated with benefits and harms”. They further state that as the data was gathered from non-randomised studies, randomized controlled trials were required and existing results should be interpreted with caution.
In the developing world, our decisions need to be tailored to the availability of facilities and the “repeat elective LSCS versus VBAC debate” should take a backseat to the prevention of obstructed labor. The WHO review recommends formulation of stringent guidelines to ensure that misoprostol is used in safe dosages for labor induction in resource –poor settings to prevent iatrogenic ruptures. Ensuring reduction of unwanted pregnancies, especially in women with high parity, and providing safe access to emergency obstetric care, should be our top priorities.
We are pleased to present our readers with the September issue of the journal, wherein two cases highlight the risk factors for rupture uterus. In cases with congenital anomalies, the uterine musculature varies in thickness in different parts of the uterus, and the abnormal portion tends to become thin as pregnancy advances; an extremely high incidence of rupture (8 %) has been reported. When pregnancy implants in a rudimentary horn, rupture usually occurs remote from term in the majority of cases.