1. Previous cesarean delivery with classical or T-shaped incision, single-layer suture of the uterine incision, and less-than-full-term cesarean delivery may increase the risk of uterine rupture in a second pregnancy.
2. The evidence is inconsistent as to how long at least the interval between previous cesarean deliveries before another pregnancy produces the least risk to the mother and child.
3. The relationship between the number of cesarean deliveries and uterine rupture is unclear.
4. The risk of placenta praevia and placental adhesions increases significantly with the increase in the number of cesarean deliveries.
For many reasons, the cesarean delivery rate in China has been increasing year by year in the last decade, reaching 50% and even more than 60% in some areas. Cesarean delivery increases the risk of complications in the next pregnancy, such as uterine rupture, placenta praevia, placental adhesions and complications related to bleeding; and with more cesarean deliveries and a short interval between pregnancies, it further increases the risk to the mother and child. The impact of different pregnancy intervals and the number of cesarean deliveries on adverse maternal and child outcomes is particularly important in China, which is currently experiencing the peak of the first generation of one-child births and a high rate of cesarean deliveries. The risk of re-pregnancy after cesarean delivery is mainly related to the risk of uterine rupture, placenta praevia, placental adhesions, and postpartum hemorrhage, so the assessment of the risk of re-pregnancy after cesarean delivery focuses on the assessment of the factors affecting the risk: in short, the interval between pregnancies and the number of cesarean deliveries on the impact of pregnancy.
I. Factors influencing the repair of the uterine incision
The conditions at the time of the previous cesarean section have an impact on the repair of the uterine incision, which in turn affects the outcome of the mother and child in the second pregnancy, such as: the gestational week of the previous cesarean section, whether or not labor was in progress before the cesarean section, indications for the cesarean section, the type of uterine incision, the way the uterine incision was closed, and the recovery after the cesarean section.
1.Type of uterine incision.
The most commonly used incision for cesarean delivery is lower uterine transverse incision, other incisions include classical incision, T-shaped incision, lower uterine straight incision, etc. The classical incision and T-shaped incision are the most unfavorable to the healing of the uterine incision, and the incidence of uterine rupture during re-pregnancy is 4-9%, which can occur before full term, before or during labor; while the rate of rupture during re-pregnancy is 0.2-0.9% for the lower transverse uterine incision.
2. The way the uterine incision is sutured (single or bilateral, locked edge).
The effect of the way the uterine incision is sutured during cesarean delivery on the rupture of the uterus in the next pregnancy (especially when a vaginal trial of labor is performed after cesarean delivery) is still unclear. Therefore, the way the uterine sutures are closed varies from hospital to hospital and even from doctor to doctor in the same hospital. The way the uterine incision is sutured (single or double layer) has no effect on the occurrence of uterine rupture in the next pregnancy, although there is no difference in the incidence of uterine rupture, but single layer suture increases the risk of uterine dehiscence in another pregnancy!
3. Gestational week of previous cesarean delivery.
Whether the gestational week at the time of the previous cesarean delivery and the risk of uterine rupture in another pregnancy: compared to the previous full-term cesarean delivery, the risk of uterine rupture in another pregnancy increases if the previous one was not full-term!
Effect of different intervals of pregnancy on pregnancy outcome
The repair of the smooth muscle of the uterus is very slow, and the repair of the smooth muscle of the uterine incision after cesarean delivery takes a long time, and MRI and hysteroscopy revealed that the repair of the uterine incision scar is not complete 6-12 months after surgery. The risks associated with uterine rupture, such as fetal death, severe neonatal HIE, and maternal death, are increased.
An analysis of the risk of uterine rupture in a second pregnancy with cut-off points of 12, 24, and 36 months after cesarean section found that the risk of uterine rupture in a second pregnancy with a vaginal trial of labor increased 2-3 times if the interval between pregnancies was less than 24 months. If the interval between pregnancies was less than 18 months, the risk of symptomatic uterine rupture at the time of vaginal trial of labor was increased 3-fold. If the interval between pregnancies is less than 6 months, the risk of uterine rupture in a second pregnancy increases almost threefold, but an interval of 6-18 months does not significantly increase the risk of uterine rupture in a second pregnancy.
In conclusion, the evidence is inconsistent as to how long an interval after a previous cesarean delivery, at least, produces the least risk to the mother and child for a second pregnancy.
III. Effect of different number of cesarean deliveries on pregnancy outcome
The risk of serious maternal complications associated with uterine rupture, placenta praevia, placental adhesions, and hysterectomy increases with the number of cesarean deliveries.
The relationship between the number of cesarean deliveries and uterine rupture (especially the risk of uterine rupture during the trial of labor) is not well established. Most scholars believe that the risk of uterine rupture increases with the number of cesarean deliveries. The risk of uterine rupture was reported to be 0.6% in the group with a history of 1 cesarean delivery and 1.8% in the group with a history of 2 or more cesarean deliveries. As the number of cesarean deliveries increases, the uterine scars become more fragile and thus more susceptible to uterine rupture. Although there is no clear opposition to vaginal trial of labor in pregnant women with a history of 2 or more cesarean deliveries, it is suggested that the risk of uterine rupture is significantly increased. Vaginal trial of labor can be performed after cesarean delivery. Interestingly, many studies have found that the risk of uterine rupture and other complications decreases when vaginal delivery is successfully performed after cesarean delivery and that the risk of uterine rupture decreases accordingly as the number of vaginal deliveries increases.
Although uterine rupture is catastrophic, its absolute incidence is low; placenta praevia and placental adhesions, which are associated with the number of cesarean deliveries, are more common and cause severe bleeding during labor and hysterectomy, and should be taken more seriously.
Similarly, the risk of placental adhesions increases with the number of cesarean deliveries. In case of placenta praevia, the incidence of placental adhesions will be higher as the number of cesarean deliveries increases!
In addition to the increased incidence of placenta praevia and placental adhesions, other complications such as massive blood transfusion, bladder injury and cystotomy, bowel injury, ureteral injury, etc. will also increase. A corresponding increase in serious maternal complications (blood transfusion, hysterectomy, bladder injury and cystotomy, bowel injury, ureteral injury, coagulopathy, embolic disease, pulmonary edema) has been reported with an increase in the number of cesarean deliveries!
Although the incidence of serious maternal complications increases with the number of cesarean deliveries, maternal deaths associated with this increase are rare, so it is not possible to suggest a limit to the number of cesarean deliveries allowed based on the results of the current study. The timing of re-pregnancy after cesarean delivery should be determined based on the different intervals, number of cesarean deliveries, previous cesarean deliveries and the risk of various complications, as well as good follow-up and monitoring during pregnancy and delivery in order to avoid or detect various serious complications early.