Clinical Comparison of Anterior or Posterior Placental Location with Placenta Previa and History of Previous Cesarean Section Delivery

Background

Placenta previa is defined as a placenta that grows from the anterior or posterior wall of the uterus and covers the cervix. The recent rise in the incidence of placenta previa has been attributed to the increased number of cesarean sections [1,2]. In Turkey, this rate is around 8% [3]. Diagnosis of placenta previa can be made based on a standard ultrasonographic examination. In these patients, massive bleeding, organ injury or death can occur during surgery [4,5]. Thus, in these high-risk pregnancies, it is critical to determine whether the placenta is positioned anteriorly or posteriorly. In pregnant women with an anterior placenta in which placenta percreta is present and can include bladder involvement, the surgical procedure for delivery can be more complicated [6]. In addition, intraoperative bleeding occurs more often in patients with placenta previa with an anterior placenta [7]. The present study seeks to compare clinical outcomes between anterior and posterior placental location in the setting of placenta previa and history of prior cesarean section delivery. Differences in placental location may be integral for preoperative surgical preparation and intraoperative surgical management.

Material and Methods

INCLUSION AND EXCLUSION CRITERIA:

All patients had had at least 1 previous cesarean section. Patients in whom the placenta completely covered the cervical os, as determined on preoperative ultrasonography, were included in the study. Patients with a low-lying placenta and patients operated on before the 20^th week of pregnancy were excluded from the study. In addition, patients diagnosed with placenta previa were excluded from the study if they did not have a previous cesarean section.

STATISTICAL ANALYSIS:

Statistical analysis was performed using SPSS software (IBM SPSS 21.0 for Mac OS; IBM Corp., Armonk, NY). The data are presented as the mean±standard deviation or median and interquartile range. The Mann-Whitney U test or Fisher’s exact test was used to compare data between groups. A P value <0.05 was considered to indicate statistical significance. The Kolmogorov-Smirnov test was used to determine whether the data were normally distributed.

Prior to the study, approval was obtained from the ethics committee of our university (no. 2020–90). The study was conducted in accordance with the principles of the 2013 Helsinki Declaration.

Results

Of the 116 patients included in the study, 78 were in group 1 and 38 in group 2. The mean age in groups 1 and 2 was 33.8±5.1 years and 32.4±5.6 years, respectively (P=0.181). Gravida and parity were 5.4 and 3.8 in group 1 and 4.1 and 2.7 in group 2 (P=0.005 and P=0.003), respectively. The mean number of previous cesarean sections was 2.71 in group 1 and 2.01 in group 2 (P=0.002). Detailed demographic data of the patients are presented in Table 1.

The mean duration of surgery was 55.5 min in group 1 and 43.3 min in group 2 (P=0.001). The rate of invasion (percreta) was significantly higher in group 1 than in group 2 (65.4% vs 5.3% [n=512 vs n=2] P<0.001), as was the estimated blood loss (790 mL vs 527 mL, P=0.014). The total ES (during and after surgery) was significantly higher in group 1 patients (0.8 vs 0.2, P=0.014). The number of sutures used during surgery was 8.8 in group 1 vs 7.6 in group 2 (P=0.003). The postoperative hospital stay was significantly longer in group 1 than in group 2 (2.8 days longer; P=0.012). The surgical findings are presented in Table 2.

Discussion

Placenta previa, the most significant complication of pregnancy, is associated with the number of previous cesarean sections [1,2,9]. In Turkey, the number of cesarean sections is increasing, and so is the incidence of placenta previa [3]. Placenta previa can lead to life-threatening bleeding during pregnancy or at the time of cesarean section delivery, possibly requiring blood transfusion, hysterectomy, or intensive care or leading to maternal death [10–12]. Given the high risk of mortality and morbidity associated with placenta previa, localization of the placenta (anterior vs posterior) is an important step in its determination and in preoperative planning in terms of the preoperative preparation of blood products and the potential surgical procedures.

In this study, the patients were divided into 2 groups depending on placental location. In group 1, the placenta was located at the anterior wall and in group 2 at the posterior wall. In both groups, the placenta blocked the cervical os. Only patients with a previous cesarean section were included in the study, with a significantly higher number of previous cesarean sections in group 1 (P=0.002). This result implies an association of an anterior placenta with a higher number of previous cesarean sections. In another study, patients with an anterior placenta were at higher risk of invasion, which in turn was more likely in patients with a higher number of previous cesarean sections [13]. In addition, the amount of bleeding during surgery (P=0.014), duration of the surgery (P=0.001), and amount of ES given to the patient in total (P=0.014) were significantly higher in group 1 patients than in group 2 patients. The incidence of invasion was also higher in our group 1 patients (P<0.001).

Placenta previa is the most common cause of postpartum hemorrhage [9]. A study investigating severe postpartum bleeding in placenta previa identified an anterior placenta as an important risk factor [14]. In another study investigating the risk of cesarean hysterectomy, bleeding was found to be higher in patients with an anterior placenta [15]. Similar results were obtained in a study investigating the causes of massive bleeding in patients with placenta previa [16]. That study also reported previous cesarean section as a risk factor. These results are consistent with our finding of a larger volume of bleeding in group 1 patients (P=0.014).

Patients with excessive bleeding during surgery often need a blood transfusion. In this study, 4 units of ES were prepared before surgery, as described in another study [17]. Among our patients, the volume of erythrocytes transfused was higher in group 1 than in group 2 patients (0.8 units higher; P=0.014). Titapant et al [17] also reported a higher rate of blood transfusion in patients with an anterior placenta and identified both multiparity and previous cesarean section as risk factors. In contrast to our study, the latter study included patients who had not had a previous cesarean section.

In a study investigating the risk factors for antepartum bleeding in patients with placenta previa, an anterior placenta, but not a posterior placenta, was found to be a risk factor for antepartum hemorrhage [18].

Most studies in the literature have evaluated only the amounts of blood transfused. This was not the case in our study, which also considered the number of patients given ES. In this study, while the need for intraoperative blood was the same in both groups, the total ES needed (intraoperative and postoperative) was 35% higher in group 1 (P=0.015). Although 4 units of ES are prepared for all patients with a diagnosis of placenta previa, blood products are not needed for most patients.

In a study comparing uterine incision methods in patients with placenta accreta spectrum, both the invasion rate and the estimated amount of bleeding were higher in the group with an anterior placenta. In these patients, the operation time was significantly longer and more ES units were used [19].

The duration of cesarean section surgery is longer in patients with placenta previa than in those without [20,21]. In the present study, the duration of surgery was significantly longer in the group with an anterior placenta (P=0.001). This suggests that additional time was needed to stop the bleeding in those patients with more blood loss.

A larger number of intraoperative sutures was needed in group 1 (8.8 sutures) than in group 2 (7.6 sutures), with P=0.003. This number was still smaller than that reported in a previous study (14.5 sutures) [21], but similar reports are lacking.

In our study, the rate of invasion (percreta) was significantly higher in group 1 than in group 2 (65.4% vs 5.3%, P<0.001). In addition, the duration of surgery, amount of bleeding, volume of transfused ES, and number of sutures were significantly higher in these patients. In a study evaluating patients with placenta accreta spectrum, bleeding was more common in patients with an anterior placenta [1]. In a study investigating the risk of severe postpartum bleeding, an anterior placenta was identified as a risk factor. The number of patients with placental invasion was also significantly higher in the group with massive bleeding [7]. In a study of the risk of antepartum bleeding, the rate of placental invasion was significantly higher in the group with massive bleeding [18].

In our study, it is seen that placental invasion rates are higher than those of previous studies. We did not find any data to explain the reason for this. However, in our clinic, if there is at least one previous cesarean section in placenta previa patients, we prepare as if there is placental invasion. As a result, the high rate of invasion supports the necessity of preoperative preparation. This information shows us that more studies are needed on placental invasion rates.

The hospital stay is generally longer in patients with placenta previa, and specifically in those with an anterior placenta [1,21]. Similarly, patients in group 1 had a longer postoperative hospital stay (2.8 days longer) than did those in group 2 (P=0.012).

One of the limitations of our study was to study a subject with a relatively low incidence, such as placenta previa. Another is that it is a single-center study. We think that multicenter studies with more patients will contribute to the literature.

Conclusions

The location of the placenta is critical in patients with placenta previa, particularly in those who have had a previous cesarean section, as it can determine the risk of postpartum bleeding. It is therefore crucial to determine the position of the placenta before surgery to inform patients about the risk of bleeding and to prepare the blood products that might be needed during surgery. The presence of placental invasion, amount of bleeding, and number of sutures required will vary depending on the placental location. Thus, during routine prenatal care, ultrasonography should be used to check for placenta previa as well as for the anterior or posterior placement of the placenta.