UR in pregnancy is rare, but when it occurs the consequences can be life-threatening to both mother and fetus [13, 14]. The occurrence of UR varies in different parts of the world. Globally, the incidence of UR is 0.07% with the tendency of being lower in developed countries than developing countries . The rate of UR in our study was 0.0196%, consistent with the rate of developed countries. There were no cases of maternal death due to UR in our study.
There has been wide variation in the aetiology UR over years[16–18], where the increase rate of TOLAC and the use of uterotonics have created the two most common predisposing factors in the developed countries[9, 15, 19, 20]. However, the major causes of UR in developing countries are both obstetric and non-obstetric multitude of factors: multi-gravidity, teen-age pregnancy, old primi, poor socio-economic status, previous cesarean section scar, unsupervised labor and unwise use of uterotonic agents.
Our study showed that the key risk factor of UR was the presence of scar, and previous cesarean section is the most important cause of uterine scarring. Therefore, to reduce UR rate, we need to strictly control the indication of cesarean section so as to reduce the rate of cesarean section. Globally, cesarean delivery rates have been steadily increasing over the past 20–30 years[21–23]. A major contributor to this has been elective repeat cesarean sections. Approximately one-third to half of elective cesareans are performed because of a history of cesarean delivery[21, 24, 25]. Routine elective repeat cesarean section for all women with a prior cesarean section is not universally advocated, desired, or without risk. Furthermore, multiple cesarean sections also carry the increased risk of placenta previa and placenta accrete with future pregnancies. And such a policy would result in significant financial cost . However, VBAC limited such problems. As another mode of birth after caesarean section, VBAC is associated with fewer complications, such as shorter maternal hospitalization, less blood loss, and a decreased incidence of puerperal infections and thrombotic events. TOLAC is a safe option for most people and 75% women may be successful.Recent years, VBAC has been supported as a way to decrease related complications and slow the increase in cesarean births to some extents. In Norway, all mothers with one previous caesarean section are offered a chance of TOLAC unless there is an absolute contra-indication. The TOLAC rate is high with 51%, and 80% succeed. VBAC is being advocated by more and more countries, but in China, the VBAC rate was only 9.6% in 2016, as compared to 12.4% in the United States in the same year[31, 32].While TOLAC is accepted practice in hospitals with advanced medical equipment and obstetric skills, it is still controversial. A successful VBAC is associated with fewer complications compared with elective repeat cesarean delivery, whereas a failed TOLAC is associated with more complications. We can see TOLAC has gone through three stages in US. Stage one, VBAC rates had increased from 5% in 1985 to 28.3% by 1996 as recommendations favored TOLAC; Stage two, the VBAC rate had decreased to 8.5% by 2006 as the number of UR and other complications related to TOLAC increased. Some hospitals stopped offering TOLAC altogether; Stage three, VBACs had been on the rise again since 2016 and increased to 13.3% by 2018, when a balance between TOLAC and safety was reached[32, 33]. U.S experience is worth learning and most part of China is going through the stage two, so we can see the reversal of the VBAC. Therefore, promoting TOLAC in China and ensuring the safety is needed. In our study, we were expecting UR rates to be higher as people attempted a TOLAC increased. However, this was not the case here and ruptures occurring after TOLAC were not more serious. Our hospital is one of the three hospitals with the largest number of births in China, and Shanghai is one of the most advanced medical treatment areas in China, which is close to developed countries, so we have rich medical experience to reduce the occurrence of UR and ensure the maternal and perinatal safety. Our study provides evidence that under the condition of strict control and indication, TOLAC is safe and reliable and worth carrying out. With the implementation of the policy of encouraging birth in China, more and more second-child pregnant women choose to attempt a TOLAC, the rate of cesarean section and consequent risk of UR will decline as a whole, and the national medical burden and financial expenditure can be reduced.
The other two causes of uterine scarring in our study are previous myomectomy and previous cornual pregnancy. All our cases with a previous myomectomy surgery were performed by laparoscopy. With the rise of minimally invasive techniques, laparoscopic surgeries are being performed in greater numbers today than ever before. Despite overwhelming evidence that laparoscopic myomectomy is minimally invasive and associated with fewer perioperative complications, there is one concern that is still under debate, i.e., does laparoscopic myomectomy increase risk of subsequent UR? Some previous studies showed there was no difference between laparoscopic and open myomectomy on the risk of UR while others demonstrated that laparoscopic procedure increased this risk compared to open approach because it was believed to result in incompletely repaired muscle defects[34–37]. The use of powered instruments, limited instrumentation use and impossibility of palpation might be the reasons. Some techniques including multi-layer closure of the myometrium and limited use of electrosurgical energy should be adhered to by surgeons to decrease the risk. In our study, it seems to lead to more serious outcomes regarding the six UR cases following laparoscopic myomectomy. Among them four had excessive blood loss above 2000 ml and presented signs of hemorrhagic shock, three had the worst outcome, i.e., the fetuses did not survive. They might even be influenced by long-term sequelae, which can adversely affect subsequent pregnancies. The removed myoma size and number in UR patients were within average range of normal cases of laparoscopic myomectomy, which is consistent with other studies[37, 38].And there is no evidence indicating the best contraception period prior to pregnancy after myomectomy to avoid UR. Currently this interval varies by facility .Some suggested 12 months might be adequate while others concluded there was no safe interval[34, 38, 39]. In our study, the only UR case without serious complication after laparoscopic myomectomy had an interval for nine years, which is the longest. Thus, it seems to keep the duration of the contraception period longer will be safer for patients with a history of laparoscopic myomectomy. Therefore, clinicians must remain vigilant, particularly in patients with a history of laparoscopic myomectomy. And whatever the cause of scar uterus, special monitoring is needed during pregnancy and childbirth to ensure the health of the mother and newborn.
In contrast to UR in women attempting TOLAC, the UR in women with unscarred uteruses occurs often completely unexpectedly. We found an incidence of UR among women with no previous uterine scar was 3/209112 deliveries, which was in agreement of the incidence found by Thisted et al based on data from the Danish Medical Birth Registry. All three UR cases in our study were uncompleted UR found during the cesarean section with almost the same maternal and fetal complications rates as scarred uterus. Among them, two (2/3) were multiple pregnancy with uterus contraction before the cesarean section, one fell to birth vaginally because of obstructed labour. Our findings suggest that multiple pregnancy and obstructed labour are two major risk factors for UR in patients without a history of previous uterus surgery, which is in line with the recent reports published by Gibbins et al, Vandenberghe et al and Vilchez et al [40–42].
Timely detection of UR is conducive to improving maternal and infant outcomes. Symptoms are the only indicators that change dynamically, which can provide first-hand information for the doctors. In the past, caregivers were taught to look for classic signs such as sudden tearing uterine pain, vaginal hemorrhage, cessation of uterine contractions, Bandl’s ring and regression of the fetus[43, 44]. However, some studies have shown that these signs are not specific and often absent[43, 45]. Our study shows that the change of the fetal heart rate is the most reliable presenting clinical symptom. Most of the cases also presented with abnormal pain and vaginal bleeding. Alertness to these signs is the key to the timely rescue and successful management. Other studies have the same conclusions consistent with ours[43, 45].
The most common site of rupture was in the lower uterine segment (58.5 %) in our study, which was the scar site of the previous cesarean section. This result is consistent with the findings of the study done by Rizwan et al, in which 80 % of the rupture was observed in the lower uterine segment.
Our study has several strengths: (1)a population-based single-centered study, (2) covering a large period between 2013 and 2020, (3) Because all patients delivered in a medical institution, we have a complete and systematic review of all medical records. All patients were followed up six weeks after delivery and no serious complications were found after discharge. Also, the study is limited to Shanghai subjects and has limitations owing to the retrospective design. It only represents the level of developed regions in China. The situation in other parts of china is still unknown, so further research is needed to understand the generalizability of the study findings.
In conclusion, UR is a disastrous and fatal event for obstetricians and patients. In order to reduce maternal and infant mortality, obstetricians should give enough attention to the pregnant women with high risk factors by strengthening the monitoring. TOLAC is a safe and worth promoting type of delivery for the patients, and still has a long way to go in Shanghai and China.