Principal findings of this study
Prior studies have shown that PP was significantly associated with a range of adverse outcomes for both mothers and neonates; however, comparisons of PP with and without coverage of a uterine scar were rarely reported. Thus, the aim of our study was to investigate the maternal and neonatal outcomes of PPCS and Non-PPCS in a Chinese cohort. This large retrospective cohort study of 738 women with PP between January 2012 and March 2017 found that the PPCS group had poorer maternal and neonatal outcome for intraoperative blood loss, bleeding within 2 – 24 hours after delivery, postpartum hemorrhage, transfusion and fetal distress than the Non-PPCS group, even after being grouped according to whether they were complicated with AIP. Overall, infant weight, intrauterine death, postpartum anemia, oligohydramnios and number of days in the hospital were not associated with the incidence of PPCS.
China’s family planning policy has been in place for more than three decades, and most couples have been restricted to only one child since 1980. Many pregnant women have had a primary cesarean section on account of only one child being allowed. Rising primary cesarean delivery rates strongly affect maternal mortality rates due to the increase of placenta previa and accreta after multiple cesareans. With the rapid growth of the aging population, China relaxed its more than three-decade-old family planning policy and allowed a couple to have two children. A survey of maternal and child health in Asia by the WHO showed that the rate of cesarean section in China was 46.2% in 2010, which is the three times (15%) the WHO’s recommended upper limit [21]. Another study [22] recently found that the cesarean section rate rose from 28.8% in 2008 to 34.9% in 2014. However, this proportion varies widely in the 31 provinces of China from 4% to 62.5% in 2014. The high cesarean delivery rate is associated with an increased risk of placenta previa in subsequent pregnancies. This risk of PP rises as the number of prior cesarean sections increases. With the implementation of the universal two-children policy in China, there will be more multipara with a scarred uterus and PPCS in the future.
PP is suspected and diagnosed in approximately 5% of pregnancies between 15 and 16 weeks [23], and almost 90% of PP resolves to a normal position by term [24], which may be explained by the elongating of the uterus and the gradually rising position of the placenta away from the cervix with increasing gestational age. However, such a mechanism will be interfered with if the placenta is covered in uterine scarring from a previous CS such that the placenta cannot move normally. Moreover, our data showed that nearly half (47.2%) of PPCS pregnancies combined with AIP, suggesting that we should do detailed prenatal check-ups, including ultrasound and MRI when we find this condition in clinical practice, to determine the likelihood of placenta implantation, location and depth of placenta accreta.
The correlation between gestational age and different types of placenta previa remains controversial. Some studies reported no differences in gestational age at delivery of infants born to mothers with different types of placenta previa [10, 25]. However, more studies agreed that premature delivery was more frequent in women with complete placenta previa [17, 26], but the comparison of preterm birth rates between infants with mothers with PPCS and Non-PPCS is rarely reported. Our results found that premature birth remains a major problem, with 54.8% of infants born prematurely to women in the Non-PPCS group and 68.1% of infants born to women in the PPCS group.
Some studies have addressed whether types of placenta previa are associated with the severity of symptoms in mothers and neonates, but data aimed at understanding PPCS were insufficient. Our results show that women with PPCS had a higher rate of CS, postpartum hemorrhage, transfusion, and hysterectomy and that the infants born to women with PPCS had lower Apgar scores at 1 and 5 min. Specifically, women in the PPCS group are at an approximately 3-fold (48.8% vs 15.7%) increased risk of postpartum hemorrhage, and 6-fold (3.0% vs 0.5%) increased risk of hysterectomy than women in the Non-PPCS group. Additionally, the presence of accreta is often the factor that determines a change in clinical management and outcome. We divided the subjects into an AIP group and non-AIP group and found that obstetric hysterectomy was performed in 6.3% and 2.8% of the women with PPCS and Non-PPCS, respectively, in the AIP group, while it was performed in 0% and 0.2% of the women with PPCS and Non-PPCS, respectively in the non-AIP group. Prior studies simply compared the hysterectomy rates between the two AIP groups but did not perform subgroup analysis based on the type of placenta implantation. Nevertheless, our results showed that the proportion of women with hysterectomy was lower than that reported in most other studies. Ling Li [16] reported that the hysterectomy rate was 8.47% in women with PPCS and 0% in women with Non-PPCS. Another study [27] in China reported hysterectomy rates were 11.9% (12/101) and 0.8% (3/369) in women with PPCS and Non-PPCS, respectively. However, there is also a report of a very low hysterectomy rate from Israel, which stated that only 1.2% of mothers with PP underwent a hysterectomy [28]. One possible and important reason for the low hysterectomy rate in our study is that obstetricians in our hospital use a random placenta margin incision [29] (also calledan Ar’s incision), and we have found it may be a potentially valuable surgical procedure to control intraoperative and postoperative bleeding in pregnancies with complete placenta previa. We believe that retaining the uterus is of great significance to young women who desire to preserve fertility, so it is acceptable to have an increased risk of postpartum hemorrhage and postpartum transfusion in women with PPCS if we can preserve the uterus.
Studies have shown that women who conceived with assisted reproductive technology (ART) procedures had an increased incidence of placenta previa regardless of the type of ART procedure [30, 31]. The mechanism for the development of the relationship between IVF-ET and PP is uncertain. One explanation is that ART procedures, maternal factors associated with sterility or a combination of both may increase the risk of PP in ART pregnancies. Varying theories have been developed around the effects of hormones on the endometrium, the effects of embryo transfer and the effects of changes in uterine contraction wave patterns [32].There was no significant difference in IVF-ET between the PPCS and Non-PPCS groups because IVF-ET is a potential confounding factor, both HDCP and diabetes or GMD.
Strengths and limitations of the study
This is one of the largest studies investigating risk factors and clinical outcomes for PPCS and Non-PPCS placenta previa from a single medical center. The largest strength of this study is that the large sample size allowed us to study the association of PPCS and Non-PPCS and maternal and neonatal outcomes. However, there are several potential limitations to this study. First, despite this hospital being the largest maternity and child health care hospital in Foshan, selection bias is likely because this is a single-center study and because this is a retrospective review that relied on medical documentation and a database. Second, although we used ultrasound or MRI to distinguish between the front and back walls of the placenta, the division is not very precise since we did not measure the area of the anterior or posterior placenta walls. Larger studies are needed to determine the safety and efficacy of interventional radiology before this technique can be recommended for routine management of placenta implantation [33]. Therefore, this study does not use the following procedures: intraoperative internal iliac artery and/or postoperative uterine artery embolization and internal iliac artery or abdominal balloon occlusion. It would be prudent to compare hospitals at different levels or in different regions due to the presence of different surgical instruments, surgical procedures, hemostasis procedures, surgical physician levels, and anesthetics. All of these potential limitations should be considered when interpreting the results of this study.