Link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7161269/
Title: Effect of Previous Placenta Previa on Outcome of Next Pregnancy: A 10-Year Retrospective Cohort Study
Citation: Zhang, L., Bi, S., Du, L., Gong, J., Chen, J., Sun, W., Shen, X., Tang, J., Ren, L., Chai, G., Wang, Z., & Chen, D. (2020). Effect of previous placenta previa on outcome of next pregnancy: a 10-year retrospective cohort study. BMC pregnancy and childbirth, 20(1), 212. https://doi.org/10.1186/s12884-020-02890-3
The article explains that placenta previa can results in physiological changes to the uterus, such as scar formation, endometrial damage, defective decidualization, and inflammation, which can all theoretically have an adverse effect on the outcome of subsequent pregnancies. Additionally, risk factors for placenta previa on their own can also influence subsequent pregnancy. The purpose of this study is to determine whether a history of placenta previa is in fact linked to adverse outcomes in subsequent pregnancy, as theorized.
The study used a 10-year retrospective cohort study of pregnant women from 2009 to 2018. The woman were divided up into a C-section delivery group and vaginal delivery group during the first pregnancy. They were then further divided into placenta previa, versus no placenta previa. Adverse maternal outcomes following history of placenta previa in the study included postpartum hemorrhage, blood transfusion, placenta accrete/increta/percreta, placenta previa, hysterectomy, ICU admission, puerperal infection, and maternal mortality. The results of the study showed that a history of placenta previa was an independent risk factor for placenta accrete and placenta previa during subsequent pregnancy in both C-section and Vaginal Delivery groups. Furthermore, within the C-section group, palcenta previa history increased the risk of postpartum hemorrhage during subsequent pregnancy. The article notes that palcenta previa and accrete share common risk factors, including disruption of the endometrium, manual removal of the placenta, and uterine scarring due to intrauterine and intraoperative procedures / other gynecological surgeries. A placenta located in the lower segment of the uterus influences the contraction of th uterus and its ability to compress the blood vessels, leading to bleeding nad more intrauterine intra-op procedures, which in turn results in uterine scar formation and pelvic adhesions. Those areas of scarring will have poor vascularization, deficient tissue oxygenation, and inflammation, which can leade to abnormal placental attachment and location. Therefore, abnormal implantation and development of the placenta have been found in subsequent pregnancies of women with a history of previa.
The risk of postpartum hemorrhage in women with history of placenta previa was found to be 2.25 times greater than women without that history in the C-section group; however, in the Vaginal Delivery group a history of previa did not increase the risk of post-partum hemorrhage. During C-section delivery, more intrauterine procedures were needed in the patients from the C-section group, and damage to the uterus was more severe, which in turn increased risk for placenta previa and accrete in subsequent pregnancies, as mentioned. Additionally, an abnormal placenta (previa, accreta) can potentially result in life-threatening hemorrhage. However, the study showed that a history of previa did not increase the risk of blood transfusion, because the effect of previous previa on postpartum hemorrhage was mild-moderate, and many women with postpartum hemmorhage did not need blood transfusions.
The article notes some limitations to the study, which include the study deisgn (retrospective study). The study was also vulnerable to referral bias since it was based in a tertiary hospital that specialized in the treatment of women with pregnancy-related illnesses referred from other areas. It’s also difficult to prove the actual mechanism of why pregnant women with placenta previa were at risk for the adverse outcomes in subsequent pregnancies based on the results alone. Future studies should therefore examine the effects of history of previa on the outcomes of subsequent pregnancies.
The article concludes that pregnant women with a history of placenta previa are at risk for adverse outcomes such as postpartum hemorrhage, placenta accrete, and placenta previa in subsequent pregnancy. The article recommends obstetricians to advise these patients about the risks involved and undertake careful perinatal surveillance for these patients.
