Circulating tumor DNA in liquid biopsy: Current diagnostic limitation

With the rapid development of science and technology,cell-free DNA(cfDNA)is rapidly becoming an important biomarker for tumor diagnosis,monitoring and prognosis,and this cfDNA-based liquid biopsy technology has great potential to become an important part of precision medicine.cfDNA is the total amount of free DNA in the systemic circulation,including DNA fragments derived from tumor cells and all other somatic cells.Tumor cells release fragments of DNA into the bloodstream,and this source of cfDNA is called circulating tumor DNA(ctDNA).cfDNA detection has become a major focus in the field of tumor research in recent years,which provides a new opportunity for non-invasive diagnosis and prognosis of cancer.In this paper,we discuss the limitations of the study on the origin and dynamics analysis of ctDNA,and how to solve these problems in the future.Although the future faces major challenges,it also con-tains great potential.

Clinical Value of Peripheral Blood Circulating Tumor Cells and Cell-Free DNA Combined Detection in Triple-Negative Breast Cancer

Objective:To determine the clinical value of combined detection of circulating tumor cells(CTCs)and cell-free DNA(cfDNA)in peripheral blood of patients with triple-negative breast cancer.Method:41 patients with breast cancer admitted to the First Central Hospital of Baoding from January 2020 to December 2021 were selected and recruited into the experimental group,42 patients with benign breast cancer admitted during the same period were recruited into the conditional control group,and 41 healthy patients admitted during the same period were recruited into the blank control group.The positive rate of peripheral blood CTCs,the level of cfDNA,and the diagnostic efficacy of peripheral blood CTCs,cfDNA alone and the combination thereof for breast cancer were analyzed.Result:The positive rates of peripheral blood CTCs in the experimental group,the conditional control group,and the blank control group were 43.90%,11.90%,and 9.74%,respectively,and there was significant difference among the groups.The levels of cfDNA in peripheral blood of the experimental group,the conditional control group,and the blank control group were 0.26±0.08 bp,0.17±0.03 bp,and 0.15±0.04 bp,respectively,which were statistically significant.The detection levels of 100 bp hTERT/ng mT1 and 241 bp hTERT/ng-mT1 in the experimental group were significantly higher than those in the conditional control group and the blank control group.The accuracy of peripheral blood CTCs detection in the three groups was 66.21%,the accuracy of cfDA241 bp/100 hp hTERT detection was 80.41%,and the accuracy of combined detection of peripheral blood CTCs and cfDNA was 94.03%.Conclusion:The clinical application of peripheral blood CTCs combined with cfDNA level detection can increase detection accuracy,provide data support for clinicians,and improve the clinical diagnostic effect of triple-negative breast cancer.

Non-invasive Prenatal Gene Diagnosis: Progress through Cell-free Fetal DNA and RNA in Maternal Plasma and Urine

Non-invasive prenatal gene diagnosis has been developed rapidly in the recent years, and numerous medical researchers are focusing on it. Such techniques could not only achieve prenatal diagnosis accurately, but also prevent tangential illness in fetuses and thus, reduce the incidence of diseases. Moreover, it is non-invasive prenatal gene diagnosis that prevents potential threaten and danger to both mothers and fetuses. Therefore, it is welcomed by clinical gynecologist and obstetrian, researchers of medical genetics, and especially, pregnancies. This review article touches briefly on the advanced development of using cell-free DNA, RNA in maternal plasma and urine for non-invasive prenatal gene diagnosis.

Circulating tumor DNA for diagnosis,prognosis and treatment of gastrointestinal malignancies

Minimally invasive detection of circulating tumor DNA(ctDNA)in peripheral blood or other body fluids of patients with gastrointestinal malignancies via liquid biopsy has emerged as a promising biomarker.This is urgently needed,as conventional imaging and plasma protein-derived biomarkers lack sensitivity and specificity in prognosis,early detection of relapse or treatment monitoring.This review summarizes the potential role of liquid biopsy in diagnosis,prognosis and treatment monitoring of gastrointestinal malignancies,including upper gastrointestinal,liver,bile duct,pancreatic and colorectal cancer.CtDNA can now be part of the clinical routine as a promising,highly sensitive and specific biomarker with a broad range of applicability.Liquid-biopsy based postoperative relapse prediction could lead to improved survival by intensification of adjuvant treatment in patients identified to be at risk of early recurrence.Moreover,ctDNA allows monitoring of antineoplastic treatment success,with identification of potentially developed resistance or therapeutic targets during the course of treatment.It may also assist in early change of chemotherapy in metastatic gastrointestinal malignancies prior to imaging findings of relapse.Nevertheless,clinical utility is dependent on the tumor’s entity and burden.

Cell-free mitochondrial DNA quantification in ischemic stroke patients for non-invasive and real-time monitoring of disease status

BACKGROUND Acute ischemic stroke(AIS)is one of the major causes of the continuous increasing rate of global mortality due to the lack of timely diagnosis,prognosis,and management.This study provides a primitive platform for non-invasive and cost-effective diagnosis and prognosis of patients with AIS using circulating cellfree mitochondrial DNA(cf-mtDNA)quantification and validation.AIM To evaluate the role of cf-mtDNA as s non-invasive,and affordable tool for realtime monitoring and prognosticating AIS patients at disease onset and during treatment.METHODS This study enrolled 88 participants including 44 patients with AIS and 44 healthy controls with almost similar mean age group at stroke onset,and at 24 h and 72 h of treatment.Peripheral blood samples were collected from each study participant and plasma was separated using centrifugation.The cf-mtDNA concentration was quantified using nanodrop reading and validated through real-time quantitative polymerase chain reaction(RT-qPCR)of NADH-ubiquinone oxidoreductase chain 1(ND1)relative transcript expression levels.RESULTS Comparative analysis of cf-mtDNA concentration in patients at disease onset showed significantly increased levels compared to control individuals for both nanodrop reading,as well as ND1 relative expression levels(P<0.0001).Intergroup analysis of cf-mtDNA concentration using nanodrop showed significantly reduced levels in patients at 72 h of treatment compared to onset(P<0.01).However,RT-qPCR analysis showed a significant reduction at 24 h and 72 h of treatment compared to the disease onset(P<0.001).The sensitivity and specificity were relatively higher for RT-qPCR than nanodrop-based cfmtDNA quantification.Correlation analysis of both cf-mtDNA concentration as well as ND1 relative expression with National Institute of Health Stroke Scale score at baseline showed a positive trend.CONCLUSION In summary,quantitative estimation of highly pure cf-mtDNA provides a simple,highly sensitive and specific,non-invasive,and affordable approach for real-time monitoring and prognosticating AIS patients at onset and during treatment.

Role of circulating free DNA in colorectal cancer

The gradual elucidation of the underlying biology of colorectal cancer has provided new insights and therapeutic options for patients with metastatic disease which are selected according to predictive biomarkers. This precision medicine paradigm, however, is incomplete since not all eligible patients respond to these agents and prognostic stratification is largely based on clinicopathologic variants. Importantly, no robust data exist to help properly select patients with localized disease at high risk for recurrence and most likely to benefit from adjuvant chemotherapy. There is a rapidly expanding body of literature regarding the role of the qualitative and quantitative analysis of circulating free DNA in various neoplasms, which consistently outperforms traditional tumor markers both as a predictive and as a prognostic marker. Several lines of evidence suggest that circulating free DNA may exhibit a complementary role to existing modalities for the early diagnosis of colorectal cancer, the selection of patients for adjuvant chemotherapy, for the followup of treated patients, for the selection of treatment for advanced disease and the assessment of response and for determining the prognosis of patients. These data, which are reviewed here, illustrate the important role that circulating biomarkers may soon have at the daily clinical practice.

The Prognostic Value of Cell-Free DNA in Advanced Non-Small-Cell Lung Cancer

Background: Cell-free DNA (cfDNA) holds promise as a tumor marker of clinical importance. We aimed to investigate the prognostic value of baseline cfDNA in non small-cell lung cancer (NSCLC). Material and Methods: During a three-year period, patients with newly diagnosed, previously untreated advanced NSCLC were included in a consecutive, prospective marker-trial. Plasma was isolated from a pre-treatment peripheral blood sample and the level of total cfDNA was measured by an in-house assay qPCR-method. The treatment comprised carboplatin (AUC 5) intravenously day 1), and vinorelbine (30 mg/m2 intravenously day 1 and 60 mg/m2 perorally day 8) q3w for a maximum of six cycles. The primary end-point was overall survival (OS). Secondary end-points were progression free survival (PFS) and overall response rate (ORR). Results: 245 patients were included and received a minimum of 1 cycle of chemotherapy (median 4). The median OS was 8.9 months, the median PFS by intention to treat 5.4 months and the ORR was 25%. The patients were divided into four groups based on quartiles of cfDNA and subsequently dichotomized by the 75th percentile revealing a significantly worse prognosis for patients in the upper 75th percentile (median OS 4.9 months) compared to patients with lower levels (10.0 months) (HR 2.1, 95%CI 1.4 - 3.1, p 0.0001). A multivariate analysis confirmed the independent prognostic value of cfDNA. A subgroup analysis of patients with high cfDNA and poor performance status (PS = 2) identified a group of patients with even worse prognosis (median OS 2.0 versus 9.1 months, HR 3.6, 95%CI 1.4 - 9.2, p 0.0001). Similar and significant results were found when comparing level of cfDNA and PFS. Conclusions: High pre-treatment level of cfDNA seems to have a strong prognostic impact in patients with newly diagnosed advanced NSCLC. Combined with PS it identifies a patient group with minimal or no benefit of chemotherapy.

Role of cell-free DNA for predicting incidence and outcome of patients with ischemic stroke

Early diagnosis and prognosis of ischemic stroke remains a critical challenge in clinical settings.A blood biomarker can be a promising quantitative tool to represent the clinical manifestations in ischemic stroke.Cell-free DNA(cfDNA)has recently turned out to be a popular circulating biomarker due to its potential relevance for diagnostic applications in a variety of disorders.Despite bright outlook of cfDNA in clinical applications,very less is known about its origin,composition,or function.Several recent studies have identified cell-derived mitochondrial components including mitochondrial DNA(mtDNA)in the extracellular spaces including blood and cerebrospinal fluid.However,the time course of alterations in plasma mtDNA concentrations in patients after an ischemic stroke is poorly understood.DNA is thought to be freed into the plasma shortly after the commencement of an ischemic stroke and then gradually decreased.However,the importance of cell-free mtDNA(cf-mtDNA)in ischemic stroke is still unknown.This review summarizes about the utility of biomarkers which has been standardized in clinical settings and role of cfDNA including cfmtDNA as a non-invasive potential biomarker of ischemic stroke.

Prognostic and predictive blood biomarkers in gastric cancer and the potential application of circulating tumor cells

Gastric cancer(GC), with its high incidence and mortality rates, is a highly fatal cancer that is common in East Asia particularly in China. Its recurrence and metastasis are the main causes of its poor prognosis. Circulating tumor cells(CTCs) or other blood biomarkers that are released into the circulating blood stream by tumors are thought to play a crucial role in the recurrence and metastasis of gastric cancer. Therefore, the detection of CTCs and other blood biomarkers has an important clinical significance; in fact, they can help predict the prognosis, assess the staging, monitor the therapeutic effects and determine the drug susceptibility. Recent research has identified many blood biomarkers in GC, such as various serum proteins, autoantibodies against tumor associated antigens, and cell-free DNAs. The analysis of CTCs and circulating cell-free tumor DNA(ctDNA) in the peripheral blood of patients with gastric cancer is called as liquid biopsy. These blood biomarkers provide the disease status for individuals and have clinical meaning. In this review, we focus on the recent scientific advances regarding CTCs and other blood biomarkers, and discuss their origins and clinical meaning.

Two approaches for calculating female fetal DNA fraction in noninvasive prenatal testing based on size analysis of maternal DNA fragments

The concentration of cell-free fetal DNA fragments should be detected before noninvasive prenatal testing(NIPT).The fetal DNA molecules have significant clinical potential in determining the overall performance of NIPT and clinical interpretation.It is important to measure fetal DNA fraction before NIPT.However,there is still little research on how to calculate the concentration of female fetuses.Two estimation approaches were proposed to calculate fetal DNA fraction,including the fragments size-based approach,aneuploid-based approach,which are all approaches based on chromosome segments.Based on high-throughput sequencing data,two approaches to calculate the DNA fraction of male fetuses were tested and obtained the experiment values,which were close to the actual values.The correlation coefficient of fragments size-based approach was 0.9243(P<0.0001)and the aneuploid-based approach reached 0.9339(P<0.0001).We calculated the concentration of female fetuses and obtained remarkable experimental results.We came up with two approaches for calculating the fetal DNA fraction of female fetuses.It provides an important theoretical basis for the detection of female fetal concentration in future clinical diagnosis.

Liquid biopsies:DNA methylation analyses in circulating cell-free DNA

Analysis of patient＇s materials like cells or nucleic acids obtained in a minimally invasive or noninvasive manner through the sampling of blood or other body fluids serves as liquid biopsies, which has huge potential for numerous diagnostic applications. Circulating cell-free DNA（cfDNA） is explored as a prognostic or predictive marker of liquid biopsies with the improvements in genomic and molecular methods. DNA methylation is an important epigenetic marker known to affect gene expression. cfDNA methylation detection is a very promising approach as abnormal distribution of DNA methylation is one of the hallmarks of many cancers and methylation changes occur early during carcinogenesis. This re？view summarizes the various investigational applications of cfDNA methylation and its oxidized de？rivatives as biomarkers for cancer diagnosis, prenatal diagnosis and organ transplantation monitoring.The review also provides a brief overview of the technologies for cfDNA methylation analysis based on next generation sequencing.

孕妇外周血中胎儿游离DNA在产前诊断中的应用

孕妇外周血中胎儿游离DNA的发现,为无创性产前诊断开辟了一条新途径。检测孕妇血浆中特异的胎儿DNA序列已被用于胎儿性连锁疾病鉴定、RhD血型检查和多种单基因遗传病的产前诊断;游离DNA水平的变化还可被用作某些妊娠相关疾病如先兆子、早产和胎儿染色体疾病的临床诊断新指标。本文对母体外周血中胎儿游离DNA的生化特征及其临床应用研究,进行了总结和分析。

基于RASSF1A为标志的无损性孕妇血浆中胎儿RHD-DNA检测方法的建立

目的建立基于表观遗传标志RASSF1A为标志的孕妇外周血浆中胎儿RHD-DNA检测路径,用于无损性产前胎儿RhD血型预测。方法首先采用PCR-SSP对孕妇外周血细胞基因组DNA做RHD基因多个外显子检测,以确定其RHD基因型;其次对无外显子表达或部分外显子表达的孕妇,对其外周血浆中胎儿游离的DNA采用RTPCR扩增其RHD基因exon7与10,同时扩增SRY基因;另对exon 7、10和SRY都为阴性的标本检测甲基化RASSF1A基因作为胎儿DNA存在的标志。待胎儿分娩后,将基因检测结果与婴儿血清学检测结果比对,以评价该方法的准确性。结果 57位受检孕妇中,含RHD全部外显子者有17人;3人含exon 1和10,为RHD1-CE(2-9)-D10杂化基因;37人不含外显子。后两者40名孕妇中,22人检测出SRY基因,出生胎儿均为男性;另有2人为假阴性结果。39人检测出exon 7和10,其中38人基因型结果与胎儿出生后血清学结果相符,1例假阳性结果;1人未检测到SRY、exon 7和10的标本,检测到RASSF1A证明胎儿DNA存在,且胎儿出生后证实为RhD阴性女婴。结论建立了基于RASSFIA为标志的、符合中国人RHD基因特点的RhD阴性孕妇血浆游离DNA中胎儿RHD基因的检测程序,可用于临床无损性产前胎儿RhD血型预测。

Circulating tumor cells and cell-free tumor DNA analyses in urothelial cancer using the LiquidBiopsy platform

Background:Emerging data suggested that liquid biopsy such as detection of circulating tumor cells(CTCs)and cell-free tumor DNA analysis augments the management of patients with urothelial cancer(UC).We presented our pilot experience of liquid biopsy using the Ion Torrent platform to detect CTCs and genomic alterations in UC.Materials and methods:Blood or urine samples from 16 patients were subjected to CTC and plasma/urine cell-free tumor DNA isolation for next generation sequencing(NGS)using the Ion S5 system to detect mutations among 50 oncogenes on the Ion AmpliSeq Cancer Hotspot Panel.Results:The Ion Torrent platform detected a higher number of CTCs than those in previous studies using the CellSearch^(TM)system.Overall,mutations were detected in 13/16(81.3%)patients with a median number of 18(range 12-25).NGS isolated 17 hotspot mutations from 11 genes and 41 novel genomic alterations from 24 genes,some of which are supposed to be clinically actionable.Conclusions:The Ion Torrent platform efficiently detected CTCs compared with previous reports.NGS with the present system also allowed for detection of gene alterations which are likely to be therapeutic targets and provided an attractive tool to guide personalized therapy for patients with advanced UC.

母血循环胎儿DNA在无创性产前诊断中的应用

孕妇外周血中游离胎儿DNA的发现为无创性产前诊断开辟了崭新的途径。随着有关研究的深入和检测手段的发展，母血循环胎儿DNA被越来越多地应用到对病理性妊娠和胎儿疾病的研究中，为预防和控制新生儿发病率及死亡率提供了一条快速、安全、灵敏度高、特异性强的非损伤性产前诊断方法，对优生优育、提高人口素质具有明显的社会意义。

Liquid biopsy for gastric cancer:Techniques,applications,and future directions

After the study of circulating tumor cells in blood through liquid biopsy(LB),this technique has evolved to encompass the analysis of multiple materials originating from the tumor,such as nucleic acids,extracellular vesicles,tumor-educated platelets,and other metabolites.Additionally,research has extended to include the examination of samples other than blood or plasma,such as saliva,gastric juice,urine,or stool.LB techniques are diverse,intricate,and variable.They must be highly sensitive,and pre-analytical,patient,and tumor-related factors significantly influence the detection threshold,diagnostic method selection,and potential results.Consequently,the implementation of LB in clinical practice still faces several challenges.The potential applications of LB range from early cancer detection to guiding targeted therapy or immunotherapy in both early and advanced cancer cases,monitoring treatment response,early identification of relapses,or assessing patient risk.On the other hand,gastric cancer(GC)is a disease often diagnosed at advanced stages.Despite recent advances in molecular understanding,the currently available treatment options have not substantially improved the prognosis for many of these patients.The application of LB in GC could be highly valuable as a non-invasive method for early diagnosis and for enhancing the management and outcomes of these patients.In this comprehensive review,from a pathologist’s perspective,we provide an overview of the main options available in LB,delve into the fundamental principles of the most studied techniques,explore the potential utility of LB application in the context of GC,and address the obstacles that need to be overcome in the future to make this innovative technique a game-changer in cancer diagnosis and treatment within clinical practice.

孕妇年龄、孕周及体重指数对孕妇外周血中胎儿游离DNA比例的影响

目的无创产前诊断(noninvasive prenatal testing,NIPT)是通过提取母体外周血中游离DNA,经高通量测序技术和生物信息学分析,发现游离DNA中是否存在比例异常的染色体,进而判断胎儿是否存在染色体非整倍体。孕妇外周血中胎儿游离DNA比例是影响NIPT准确性的重要因素,评价孕妇年龄、孕周和体重指数(body mass index,BMI)对胎儿游离DNA比例的影响对提高NIPT的准确性有重要意义。方法回顾性分析了2015年3月至2016年5月苏州市立医院2563例孕有正常男性胎儿孕妇的NIPT检测结果及相关数据,提取孕妇外周血胎儿游离DNA浓度、孕妇年龄、孕周和体重指数等信息,对以上参数进行了归一化处理后再进行相关性分析,挖掘孕妇年龄、孕周和BMI对孕妇外周血中胎儿游离DNA比例的影响。结果数据显示孕妇外周血中胎儿游离DNA比例与孕周呈正相关(线性回归方程y=0.003x+0.060,R2=0.752,P=0.01144);孕妇年龄与BMI也呈正相关(线性回归方程y=0.112x+18.80,R2=0.721,P=6.46E-08);而胎儿游离DNA比例与孕妇BMI、年龄均呈负相关,且在样本量较大时相关性显著。结论孕妇年龄、BMI的增加都会相对降低孕妇外周血中胎儿游离DNA的比例,孕妇年龄越大则BMI也会相对越大,而孕周的增大会提高孕妇外周血中胎儿游离DNA比例,因此,针对高龄且高BMI值的孕妇适当延后进行NIPT的孕周可以提高NIPT检测的准确性。

Noninvasive Prenatal Testing for Fetal Chromosomal Abnormalities Using Massively Parallel Sequencing: Clinical Experience from 7910 Korean Pregnancies

Objective: The purpose of this study is to review the clinical experience and performance of noninvasive prenatal testing (NIPT) method, using cell-free DNAto detect chromosomes 21, 18, 13, X, and Y abnormalities in over 7910 clinical samples from South Korean population. Method: Pregnant women between 1st of November 2015 to 18th of February 2018, with obstetric clinical findings participated in the study. NIPT was performed based on masivelly parallel sequencing with 0.3× low coverage paired-end sequencing using cell-free DNA in maternal plasma. Further invasive prenatal testing was recommended for pregnant women with positive NIPT results. Results: Of the total 7910 participants, 7890 (99.75%) were tested for NIPT and the remaining 20 (0.25%) were below the Quality Control (QC) standards. T13, T18, XXX, XXY and XYY had 100% of sensitivity, specificity, positive predictive values (PPV) and accuracy. The overall sensitivity was 100% and specificity, PPV and accuracy of all chromosomal abnormalities with further validation were 99.92%, 94.25%, and, 99.92% respectively. Conclusion: Our NIPT results showed high positive predictive value for the detection of autosomal trisomies and sex chromosome aneuploidies in our sample cohort.

Prenatal diagnosis of Down syndrome using cell-free fetal DNA in amniotic fluid by quantitative fluorescent polymersase chain reaction

Backgroud Amniotic fluid （AF） supernatant contains cell-free fetal DNA （cffDNA） fragments.This study attempted to take advantage of cffDNA as a new material for prenatal diagnosis,which could be combined with simple quantitative fluorescent polymerase chain reaction （QF-PCR） to provide an ancillary method for the prenatal diagnosis of trisomy 21 syndrome.Methods AF supernatant samples were obtained from 27 women carrying euploid fetuses and 28 women carrying aneuploid fetuses with known cytogenetic karyotypes.Peripheral blood samples of the parents were collected at the same time.Short tandem repeat （STR） fragments on chromosome 21 were amplified by QF-PCR.Fetal condition and the parental source of the extra chromosome could be determined by the STR peaks.Results The sensitivity of the assay for the aneuploid was 93％ （26/28; confidence interval,CI：77％-98％） and the specificity was 100％ （26/26; CI：88％-100％）.The determination rate of the origin of the extra chromosome was 69％.The sensitivity and the specificity of the assay in the euploid were 100％ （27/27）.Conclusions Trisomy 21 can be prenatally diagnosed by the QF-PCR method in AF supernatant.This karyotype analysis method greatly reduces the requirement for the specimen size.It will be a benefit for early amniocentesis and could avoid pregnancy complications.The method may become an ancillary method for prenatal diagnosis of trisomy 21.

人工流产次数、胎儿游离DNA与剖宫产后再次妊娠孕妇胎盘植入风险的关联性研究

目的:研究人工流产次数、胎儿游离DNA(ccf DNA)与剖宫产后再次妊娠孕妇胎盘植入风险之间的关系。方法:回顾性抽取2018年2月至2023年4月新乡医学院第一附属医院收治的189例剖宫产后再次妊娠合并胎盘植入妇女中睾丸特性蛋白Y(TSPY)为阳性的98例妇女作为观察组,另抽取同期88例剖宫产后再次妊娠未合并胎盘植入者作为对照组,两组均怀男胎(仅用于研究,未告知孕妇胎儿性别)。采用实时聚合酶链式反应法检测两组孕妇血浆TSPY水平。比较观察组与对照组,以及观察组不同胎盘植入深度患者、不同植入面积患者的既往人工流产次数及孕妇血浆TSPY-1水平。结果:观察组孕次及人工流产次数均多于对照组(P均<0.05),两组产次及剖宫产次数比较,差异未见统计学意义(P>0.05)。观察组孕妇血浆TSPY-1水平高于对照组(P<0.05)。粘连型、植入型及穿透型胎盘植入者人工流产次数及血浆TSPY-1水平比较,差异均有统计学意义(P均<0.05),其中植入型患者人工流产次数及血浆TSYP-1水平均高于粘连型,穿透型患者人工流产次数及血浆TSPY-1水平均高于粘连型与植入型(P均<0.05)。胎盘全部植入者人工流产次数及血浆TSPY-1水平均高于部分植入者(P<0.05)。结论:血浆ccf DNA水平及人工流产次数与既往剖宫产史孕妇再次妊娠胎盘植入具有一定的关联性。