前置血管破裂的诊治

前置血管破裂是产科一种急危重症疾病,往往并发于脐带帆状附着、前置胎盘、双叶胎盘或副胎盘等情况,严重威胁胎儿及新生儿的生命,影响围产儿结局。因此,产前高度怀疑前置血管时需严密的监护,及时诊断前置血管破裂和终止妊娠是改善围产儿结局的关键。     

Recent advances in the management of placenta previa

PURPOSE OF REVIEW: Despite the widespread and routine use of ultrasound to make the diagnosis of placenta previa, evidence-based classification and management strategies have failed to evolve over the years. The purpose of this review is to present the current evidence supporting the screening, diagnosis and management of placenta previa. RECENT FINDINGS: The prevalence of placenta previa is significantly overestimated due to the practice of routine mid-pregnancy scan, and many women currently undergo a repeat scan in late pregnancy for placental localization. Recent reports support limiting third-trimester scans to only those cases where the placental edge either reaches or overlaps the internal cervical os at 20-23 weeks of pregnancy. In some cases of mid-trimester placenta previa, the placental edge is more likely to "migrate" than others, and it appears that ultrasound may be useful to predict this process. At term, women with placental edge within 2 cm of the internal cervical os require a Caesarean section for delivery, whereas an attempt at vaginal birth is appropriate if this distance is more that 2 cm. Ultrasound also has a role in the diagnosis and management of both vasa previa and placenta accreta. SUMMARY: This review addresses screening for placenta previa. A simple and pragmatic ultrasound classification of placenta previa and low-lying placenta is proposed. Caesarean section is recommended for delivery in cases of placenta previa. Women with a low-lying placenta have at least 60% chance of a vaginal birth, but should be monitored for post-partum haemorrhage. Vasa previa is a rare complication but antenatal diagnosis is possible. It should particularly be suspected in in-vitro fertilization conceptions, and where the placental edge covers the os in mid-pregnancy but recedes later on. Prenatal diagnosis of placenta accreta should be based on the placental lacunae signs rather than the absence of retro-placental clear space.     

Velamentous insertion of the umbilical cord and vasa previa

We report 31 cases with velamentous insertion of the umbilical cord of whom two had coexistent vasa previa. The prevalence of the former was 0.22% and of the latter 0.014%. Perinatal mortality was low, 3.2%, but there was a high rate of complications during pregnancy, such as threatened abortion, antepartum and intrapartum bleeding, premature delivery and fetal distress. Fifteen patients underwent caesarean section. Four of the term infants were small for gestational age. One infant had congenital malformations. The two cases with vasa previa are described in detail. We conclude that velamentous insertion of the umbilical cord should be kept in mind in the differential diagnosis of fetal distress accompanied with antepartum or intrapartum vaginal bleeding.     

Diagnóstico prenatal de vasa previa

ObjectivePrenatal diagnosis of vasa previa in cord insertion anomaliesMaterial and methodWe examined six cases of cord insertion anomalies or placentation anomaliesResultsThree cases were diagnosed of vessels previous the presentation and near the internal cervical orifice. Two cases of twin pregnancy with a cord velamentous insertion of the second twin on the partition membrane, the situation of the insertions showed a clinical vasa previa of the second twin after the potential birth of the first twin. The last case showed an interplacental vascular septum, in a bilobed placenta, that was previous to the presentation and near the internal cervical orificeConclusionThe bidimensional ultrasounds, the pulsed and color Doppler studies allowed the prenatal diagnosis of the vasa previa in the asymptomatic pregnancies. Its diagnosis was based in its suspect in cases with a velamentous insertion or with a bilobed placenta. In these situations, a detailed evaluation of the relation of the amniotic umbilical vessels with the inferior uterine segment or with the uterine region previous to the fetus will allow the diagnosis of the vasa previa     

血管前置的产前超声诊断

目的探讨血管前置的高危因素和产前超声诊断的价值。 方法回顾性分析2012年1月至2014年6月就诊于广东省妇幼保健院行产前超声检查和(或)临床诊断为妊娠合并血管前置患者的超声声像图资料,并追踪妊娠结局。 结果产前超声共检出血管前置18例,其中1例脐带先露误诊为血管前置;漏诊1例。确诊为血管前置病例共计18例,其中16例(88.9%,16/18)为单胎妊娠,2例(11.1%,2/18)为三胎妊娠;合并低置胎盘9例(50.0%,9/18),帆状胎盘8例(44.4%,8/18),副胎盘2例(11.1%,2/18),球拍状胎盘2例(11.1%,2/18),单脐动脉3例(16.8%,3/18)。18例胎儿中,早产9例(50.0%,9/18),足月产8例(44.4%,8/18),1例(5.6%,1/18)因胎儿结构异常引产。产前超声检查漏诊的1例患者,足月妊娠经阴道分娩时大出血,胎儿死亡。 结论胎盘异常是血管前置的高危因素,需重视产前超声检查,及时诊断和处理,可有效避免不良妊娠结局的发生。     

前置血管围产结局130例分析

目的:探讨前置血管临床特点、孕期管理及围产儿结局。方法:回顾性分析2013年1月至2019年5月在四川大学华西第二医院分娩的130例前置血管患者临床资料,分析其临床高危因素、孕期管理及围产儿结局。结果:130例前置血管患者占我院同期分娩产妇的1.86‰。108例(83.1%)单胎,22例(16.9%)多胎,自然受孕109例(83.8%),辅助受孕21例(16.2%),其中妊娠合并帆状胎盘(68.5%)和前置胎盘(33.8%)占多数,96.2%产前诊断前置血管的患者合并至少一个高危因素。产前诊断111例,70.3%中孕期诊断,29.7%晚孕期诊断,诊断后行严密监测,入院孕周(33.7±2.2周),分娩孕周为35.0±1.6周,34~37周分娩77例。130例分娩活产儿150个,活产儿中存活145个,其出生体质量为2422.8±462.5 g,74例(51.0%)转NICU,在NICU住院时间为8(1~49)天。产前诊断组中,多胎妊娠病例的入院孕周、分娩孕周较单胎早,早产率和新生儿死亡率明显高于单胎妊娠病例(P<0.05)。产前诊断组与产时产后诊断组新生儿早产率为87.8%与55.6%(P<0.05),新生儿死亡率分别为2.4%和7.4%(P=0.220)。结论:规范产前检查、早期诊断、严密监护胎儿情况并适时终止妊娠有助于改善前置血管孕妇围产儿结局。     

Prenatal diagnosis of vasa previa

Vasa previa is a rare condition in which unsupported by the placenta, umbilical cord blood vessels runs within the placental membranes between internal os of the cervix and presenting part of the fetus. We report an antenatal diagnostic procedure and management of a patient with low-lying placenta and velamentous cord insertion near to the internal os with two large fetal blood vessels coursing between the internal cervical os and fetal presenting part. An elective cesarean section was performed at 36 weeks gestation.     

Anticipation of uterine bleeding in placenta previa based on vaginal sonographic evaluation

OBJECTIVES: The aim of this study was to predict massive uterine bleeding during pregnancy and cesarean section in women with placenta previa using transvaginal ultrasonography. METHODS: Transvaginal ultrasonography was performed prospectively at and after 28 gestational weeks with follow-up scans at 5- to 7-day intervals until cesarean section in 35 women with placenta previa. The patients were classified into 3 groups based on the following sonographic features of the placental edge in relation to the internal cervical os: type A = two thirds of the placenta from the placental center overlapping the internal os (13 cases); type B = one third of the placenta from the periphery to outside overlapping the internal os (10 cases), and type C = echo-free space (EFS) in the placental edge overlapping the internal os (12 cases). In some cases of type-A placentas, lacunae with blood flow in the placenta from the basal plate to the chorionic plate were also observed. All types were further subdivided based on the presence or absence of associated sponge-like echo (S-echo) in the wall of the uterus adjacent to the placental location. In each type, the relation with the amount of bleeding during hospitalization and preterm delivery was examined. RESULTS: Incidences of sudden massive bleeding during hospitalization were 7.7% (1/13), 10.0% (1/10), and 83.3% (10/12), in types A, B and C, respectively, being significantly higher in type C (p < 0.01). The risk of antepartum massive bleeding was also significantly higher in type C (p < 0.01). The incidence of preterm delivery due to sudden massive bleeding and the amount of bleeding during cesarean section were significantly higher in type A + S and type A + S with lacunae, respectively. CONCLUSIONS: Sonographic EFS in the lower edge of the placenta overlying the cervix indicates the risk of sudden massive antepartum bleeding. Furthermore, lacunae with sponge-like echo may also reflect the risk of massive bleeding at cesarean section. These findings warrant further observational studies to verify their clinical implications.     

Guidelines for the Management of Vasa Previa

ObjectivesTo describe the etiology of vasa previa and the risk factors and associated condition, to identify the various clinical presentations of vasa previa, to describe the ultrasound tools used in its diagnosis, and to describe the management of vasa previa.OutcomesReduction of perinatal mortality, short-term neonatal morbidity, long-term infant morbidity, and short-term and long-term maternal morbidity and mortality.EvidencePublished literature on randomized trials, prospective cohort studies, and selected retrospective cohort studies was retrieved through searches of PubMed or Medline, CINAHL, and the Cochrane Library, using appropriate controlled vocabulary (e.g., selected epidemiological studies comparing delivery by Caesarean section with vaginal delivery; studies comparing outcomes when vasa previa is diagnosed antenatally vs. intrapartum) and key words (e.g., vasa previa). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies. Searches were updated on a regular basis and incorporated into the guideline to October 1, 2008. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology assessment-related agencies, clinical practice guideline collections, clinical trial registries, and from national and international medical specialty societies.ValuesThe evidence collected was reviewed by the Diagnostic Imaging Committee and the Maternal Fetal Medicine Committee of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and quantified using the evaluation of evidence guidelines developed by the Canadian Task Force on Preventive Health Care.Benefits, Harms, and CostsThe benefit expected from this guideline is facilitation of optimal and uniform care for pregnancies complicated by vasa previa.SponsorsThe Society of Obstetricians and Gynaecologists of Canada.Summary StatementA comparison of women who were diagnosed antenatally and those who were not shows respective neonatal survival rates of 97% and 44%, and neonatal blood transfusion rates of 3.4% and 58.5%, respectively. Vasa previa can be diagnosed antenatally, using combined abdominal and transvaginal ultrasound and colour flow mapping; however, many cases are not diagnosed, and not making such a diagnosis is still acceptable. Even under the best circumstances the false positive rate is extremely low. (II-2)Recommendations

• 1.If the placenta is found to be low lying at the routine second trimester ultrasound examination, further evaluation for placental cord insertion should be performed. (II-2B)
• 2.Transvaginal ultrasound may be considered for all women at high risk for vasa previa, including those with low or velamentous insertion of the cord, bilobate or succenturiate placenta, or for those having vaginal bleeding, in order to evaluate the internal cervical os. (II-2B)
• 3.If vasa previa is suspected, transvaginal ultrasound colour Doppler may be used to facilitate the diagnosis. Even with the use of transvaginal ultrasound colour Doppler, vasa previa may be missed. (II-2B)
• 4.When vasa previa is diagnosed antenatally, an elective Caesarean section should be offered prior to the onset of labour. (II-1A)
• 5.In cases of vasa previa, premature delivery is most likely; therefore, consideration should be given to administration of corticosteroids at 28 to 32 weeks to promote fetal lung maturation and to hospitalization at about 30 to 32 weeks. (II-2B)
• 6.In a woman with an antenatal diagnosis of vasa previa, when there has been bleeding or premature rupture of membranes, the woman should be offered delivery in a birthing unit with continuous electronic fetal heart rate monitoring and, if time permits, a rapid biochemical test for fetal hemoglobin, to be done as soon as possible; if any of the above tests are abnormal, an urgent Caesarean section should be performed. (III-B)
• 7.Women admitted with diagnosed vasa previa should ideally be transferred for delivery in a tertiary facility where a pediatrician and blood for neonatal transfusion are immediately available in case aggressive resuscitation of the neonate is necessary. (II-3B)
• 8.Women admitted to a tertiary care unit with a diagnosis of vasa previa should have this diagnosis clearly identified on the chart, and all health care providers should be made aware of the potential need for immediate delivery by Caesarean section if vaginal bleeding occurs. (III-B)

     

Vasa previa and postpartum hysterectomy in maternal Rh alloimmunization

Velamentous insertion of the cord, or vasa previa, is a malady where fetal vessels tranverse membranes ahead of the fetal part. The incidence of vasa previa is 1: 2000-3000 deliveries. Fetal mortality is over 50-75%. Early diagnosis is needed because these deliveries require emergency cesarean section; it is especially more common with placenta percreta, uterine atony and hemorrhage. Intravascular infusion of red blood cells (RBCs) into the fetus is one of the most successful means of in utero therapy for severe fetal anemia caused by RBC alloimmunization. We performed four fetal intrauterine intravascular transfusions (IVT) as therapy for severe fetal anemia. The patient underwent elective cesarean section. After delivery, profound uterine atony and vaginal hemorrhage were noted and the patient underwent hysterectomy. Pathological examination of the placenta and umbilical cord documented velamentous insertion of the cord. Before intrauterine IVT a detailed US examination is necessary to exclude vasa previa or placenta previa. Uterine atony may be result after a diagnosis of placenta previa or vasa previa. Intrauterine IVT is an irreplaceable diagnostic procedure in the treatment of severe fetal anemia.     

Placental ratio and risk of velamentous umbilical cord insertion are increased in women with placenta previa

The purpose of this study was to explore the maternal risk profile and obstetric outcome in pregnancies affected by placenta previa. Retrospective case-control study involved all women (93 [0.37%] women with diagnosed placenta previa and 24,857 unaffected controls) who gave birth to singleton infants at Kuopio University Hospital between the years 1989 and 2000. Grand multiparity, infertility problems, and advanced maternal age were independent risk factors of placenta previa, with adjusted relative risks of 5.8, 3.7, and 2.4, respectively. Most women with placenta previa (88.2%) underwent cesarean delivery before term. They also more often had velamentous umbilical cord insertion (7.5%) and higher placental-to-birthweight ratios than the controls. Placenta previa was associated with risks of preterm delivery, low birthweight infants, and need for neonatal intensive care, at odds ratios of 27.7, 7.4, and 3.4, respectively. In conclusion, placenta previa is an infrequent pregnancy complication associated with multiparity, advanced maternal age, infertility problems, elevated placental ratio, and velamentous umbilical cord insertion.     

Guideline No. 439: Diagnosis and Management of Vasa Previa

ObjectiveTo summarize the current evidence and to make recommendations for diagnosis and classification of vasa previa and for management of women with this diagnosis.Target populationPregnant women with vasa previa or low-lying fetal vessels.OptionsTo manage vasa previa in hospital or at home, and to perform a cesarean delivery preterm or at term, or to allow a trial of labour when a diagnosis of vasa previa or low-lying fetal vessels is suspected or confirmed.OutcomesProlonged hospitalization, preterm birth, rate of cesarean delivery, and neonatal morbidity and mortality.Benefits, harms, and costsWomen with vasa previa or low-lying fetal vessels are at an increased risk of maternal and fetal or postnatal adverse outcomes. These outcomes include a potentially incorrect diagnosis, need for hospitalization, unnecessary restriction of activities, an early delivery, and an unnecessary cesarean delivery. Optimization of diagnostic and management protocols can improve maternal and fetal or postnatal outcomes.EvidenceMedline, Pubmed, Embase, and the Cochrane Library were searched from inception to March 2022, using medical subject headings (MeSH) and keywords related to pregnancy, vasa previa, low-lying fetal vessels, antepartum hemorrhage, short cervix, preterm labour, and cesarean delivery. This document presents an abstraction of the evidence rather than a methodological review.Validation methodsThe authors rated the quality of evidence and strength of recommendations using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach. See online Appendix A (Tables A1 for definitions and A2 for interpretations of strong and weak recommendations).Intended audienceObstetric care providers, including obstetricians, family physicians, nurses, midwives, maternal-fetal medicine specialists, and radiologists.Tweetable AbstractUnprotected fetal vessels in placental membranes and cord that are close to the cervix, including vasa previa, need careful characterization by sonographic examination and evidence-based management to reduce risks to the baby and the mother during pregnancy and delivery.SUMMARY STATEMENTS

• 1.A marginal sinus or a loop of cord above the cervix are frequent causes of an incorrect diagnosis of vasa previa (low).
• 2.Depending on gestational age when vasa previa or low-lying fetal vessels are diagnosed, these conditions will resolve closer to the time of delivery in a large proportion of women (moderate).
• 3.Most women with vasa previa have an associated risk factor (moderate).
• 4.Depending on individual patient factors, vasa previa can be safely managed on an outpatient basis in many women (moderate).
• 5.Bed rest or reduced activity does not improve outcomes in women with vasa previa and can be harmful. However, sexual intercourse/insertion of foreign bodies in vagina or rectum have potential for harm, particularly in the third trimester (low).

RECOMMENDATIONS

• 1.The physician interpreting an obstetric sonographic examination should classify fetal vessels <2 cm from the cervical os as vasa previa (strong, moderate).
• 2.The physician interpreting an obstetric sonographic examination should classify vessels between 2 and 5 cm from the cervical os as low-lying fetal vessels (conditional, low).
• 3.The obstetric sonographic provider should use transvaginal sonography with colour mapping and pulsed-wave Doppler to diagnose vasa previa or other related variants (strong, moderate).
• 4.When a diagnosis of vasa previa or low-lying fetal vessels is made remote from delivery, the obstetric care provider should confirm the diagnosis closer to the time of delivery (strong, moderate).
• 5.The obstetric sonographic provider should assess the placental cord insertion site in all women at the routine second trimester fetal anatomical scan (conditional, moderate).
• 6.The physician interpreting an obstetric sonographic examination should not diagnose an abnormality of placental morphology, location, placental cord insertion, or vasa previa before the routine second trimester obstetrical sonographic scan (conditional, moderate).
• 7.The obstetric sonographic provider should perform targeted screening for vasa previa in all women with a risk factor (strong, moderate).
• 8.The obstetric care provider should consider hospitalization in women with vasa previa at 32 weeks of gestation, and in women with additional risk factors for early delivery, such as multiple gestation or a short cervix, before 32 weeks (conditional, moderate).
• 9.In women with vasa previa and a singleton pregnancy, the obstetric care provider should perform a cesarean delivery at 35⁰ to 35⁶ weeks. They should consider an earlier delivery if there are additional risk factors for preterm delivery (strong, moderate).
• 10.In women with vasa previa and a twin pregnancy, the obstetric care provider should consider a cesarean delivery at 33⁰ to 34⁶ weeks for dichorionic twins and at 32⁰ to 33⁶ weeks for monochorionic twins. They should consider an earlier delivery if there are additional risk factors for preterm delivery, such as higher-order multiple pregnancy or a short cervix (conditional, low).
• 11.In women with low-lying fetal vessels, the obstetric care provider should consider a cesarean delivery at 37⁰ to 38⁶ weeks for a singleton pregnancy and at 36⁰ to 37⁶ weeks for dichorionic twins (conditional, low).
• 12.In women with vasa previa, the obstetric care provider should consider timely access to an operating room, an obstetrician, an anesthetist, and an appropriate neonatal intensive care unit when deciding location of admission for observation or delivery (conditional, low).

     

Inserción velamentosa extrema de cordón umbilical, sin rotura de vasa previa

Velamentous insertion of the umbilical cord appears in one out of every 100 pregnancies and can prove life-threatening for the fetus. Consequently, prenatal diagnosis through ultrasound scanning is required, at least in women with a risk of vasa previa, such as those with multiple pregnancies, in vitro fertilization, or placenta previa, who will require an elective cesarean section.We present an extreme case of velamentous insertion of the umbilical cord, in which the vascular distribution was reminiscent of a bird's cage. Surprisingly, there was no vascular injury.     

In utero laser treatment of type II vasa previa

Vasa previa, defined as fetal vessels coursing within the membranes between the presenting part and the cervix, occurs in approximately 1:2500–5000 pregnancies. Type II vasa previa consists of fetal vessels crossing over the internal os connecting a bilobed placenta or a succenturiate lobe with the main placental mass. These vessels are prone to compression during labor or may tear when membranes rupture potentially resulting in fetal exsanguination and neonatal death. This complication could be avoided altogether if the vessels could be obliterated in utero. The purpose of this communication is to report the successful in utero laser ablation of type II vasa previa at 22.5 weeks of gestation. Subsequent ruptured membranes did not result in untoward fetal consequences. Risks and benefits of this novel procedure are discussed.     

In utero laser treatment of type II vasa previa.

Vasa previa, defined as fetal vessels coursing within the membranes between the presenting part and the cervix, occurs in approximately 1:2500-5000 pregnancies. Type II vasa previa consists of fetal vessels crossing over the internal os connecting a bilobed placenta or a succenturiate lobe with the main placental mass. These vessels are prone to compression during labor or may tear when membranes rupture potentially resulting in fetal exsanguination and neonatal death. This complication could be avoided altogether if the vessels could be obliterated in utero. The purpose of this communication is to report the successful in utero laser ablation of type II vasa previa at 22.5 weeks of gestation. Subsequent ruptured membranes did not result in untoward fetal consequences. Risks and benefits of this novel procedure are discussed.     

彩色多普勒超声在诊断帆状胎盘中的应用价值

目的:探讨彩色多普勒超声对帆状胎盘的诊断价值和临床意义。方法:对2009年2月至2011年5月来我院行超声产前检查的7865例孕妇,采用彩色多普勒超声诊断仪检查,检测胎盘内血流信号和相关区域内的血流信号,重点查看胎盘脐带附着点位置的影像,了解是否有前置血管存在,并结合临床手术进行进一步确诊。结果:经产前超声检查疑诊帆状胎盘21例,胎盘血管前置2例,最后经结合临床手术确诊20例为帆状胎盘,超声误诊3例,漏诊2例。结论:彩色多普勒超声对帆状胎盘以及帆状胎盘血管前置诊断准确率高,能够在产前早期诊断,在降低围生儿死亡率方面起了积极作用。     

Risk factors for preterm delivery in patients demonstrating sonographic evidence of premature dilation of the internal os, prolapse of the membranes in the endocervical canal and shortening of the distal cervical segment by second trimester ultrasound

OBJECTIVE: To investigate the outcomes and risk factors associated with the second trimester sonographic findings of premature dilation of the internal cervical os, prolapse of the membranes into the endocervical canal and shortening of the distal segment. STUDY DESIGN: Retrospective chart review to identify patients who met the following criteria: (i) gestational age between 16 and 24 weeks; (ii) a vaginal probe ultrasound documenting dilatation of the internal os, prolapsed membranes into the endocervical canal but not extending beyond the external os, and a shortened distal cervix; and (iii) no evidence of increased uterine activity METHODS: Sonographic measurements obtained included: (i) the width of the internal os dilation; (ii) the depth of membranes prolapsed into endocervix (funneling); (iii) the distal cervical length; and (iv) the total cervical length. Patients were stratified into two groups according to gestational age at delivery: the preterm group (< 34 weeks) and the near-term group (> or = 34 weeks). RESULTS: Thirty-seven patients had complete records for analysis and their pregnancies resulted in 47 live births. Eighteen patients were stratified to the near term group and 19 were stratified to the preterm group. There were no stillborn infants and 10 neonatal deaths. Ten patients received cerclage and seven patients delivered at < 34 weeks gestational age. Risk factors found to be significant for preterm delivery included a gestational age at diagnosis of < or = 20 weeks gestation (p = 0.03), dilatation of the internal os > 1.3 cm (p = 0.04), and a composite Benham score > or = 1.0 (p = 0.02). CONCLUSIONS: The sonographic findings of premature dilatation of the internal os, prolapse of the membranes into the endocervical canal and shortening of the distal cervix are associated with a high rate of delivery < 34 weeks (51%) and neonatal death (27%).     

The association between vasa previa, multiple gestations, and assisted reproductive technology

Patients with multiple gestations, low-lying placentas, velamentous cord insertions, and history of assisted conception should be evaluated carefully for a vasa previa. Serial surveillance for signs of preterm labor and elective cesarean delivery at 34 to 35 weeks after corticosteroids for fetal lung maturity is a reasonable management strategy for vasa previa in multiple gestations.     

Guideline No. 402: Diagnosis and Management of Placenta Previa

ObjectivesTo summarize the current evidence and to make recommendations for diagnosis and classification of placenta previa and for managing the care of women with this diagnosis.OptionsTo manage in hospital or as an outpatient and to perform a cesarean delivery preterm or at term or to allow a trial of labour when a diagnosis of placenta previa or a low-lying placenta is suspected or confirmed.OutcomesProlonged hospitalization, preterm birth, rate of cesarean delivery, maternal morbidity and mortality, and postnatal morbidity and mortality.Intended UsersFamily physicians, obstetricians, midwives, and other maternal care providers.Target PopulationPregnant women with placenta previa or low-lying placenta.EvidenceMedline, PubMed, Embase, and the Cochrane Library were searched from inception to October 2018. Medical Subject Heading (MeSH) terms and key words related to pregnancy, placenta previa, low-lying placenta, antepartum hemorrhage, short cervical length, preterm labour, and cesarean. This document represents an abstraction of the evidence rather than a methodological review.Validation MethodsThis guideline has been reviewed by the Maternal–Fetal Medicine and Diagnostic Imaging committees of the Society of Obstetricians and Gynaecologists of Canada (SOGC) and approved by the SOGC Board of Directors.Benefits, Harms, and/or CostsWomen with placenta previa or low-lying placenta are at increased risk of maternal, fetal and postnatal adverse outcomes that include a potentially incorrect diagnosis and possibly unnecessary hospitalization, restriction of activities, early delivery, or cesarean delivery. Optimization of diagnosis and management protocols has potential to improve maternal, fetal and postnatal outcomes.SUMMARY STATEMENTS (GRADE ratings in parentheses)

• 1All women with placenta previa or low-lying placenta have an increased risk of a morbidly adherent placenta, particularly those who have had a prior cesarean delivery (strong/moderate).
• 2In women with placenta previa or a low-lying placenta, presence of a marginal/velamentous cord insertion close to the cervical os or a succenturiate placental lobe increases the risk of vasa previa (strong/moderate).
• 3History of antepartum hemorrhage (first episode <29 weeks or recurrent episodes [≥3]), a thick placental edge covering (or close to) the cervical os, short cervical length (<3 cm with placenta previa, <2 cm with low-lying placenta), and a previous cesarean delivery are risk factors with an associated increased risk of urgent/preterm cesarean delivery (strong/moderate).
• 4In the absence of risk factors, outpatient management of women with placenta previa is safe (strong/moderate).
• 5Bed rest or reduced activity is not beneficial in women with placenta previa and can be potentially harmful. However, sexual intercourse/insertion of foreign bodies in vagina or rectum should be avoided (conditional [weak]/low).
• 6Preoperative bedside ultrasound assessment of placental location can be useful for planning of surgical technique and may reduce risk of intraoperative transection of placenta (conditional [weak]/low).
• 7Regional anaesthesia is safe and adequate as a first-line anaesthetic approach for the peripartum management of patients with placenta previa or low-lying placenta (conditional [weak]/low).
• 8When deciding the location of delivery, consider ultrasound assessment of placental location, any risk factors, the patient's history, and logistical factors, including available resources at the delivery unit (conditional [weak]/low).

RECOMMENDATIONS (GRADE ratings in parentheses)

• 1Classify placental location as placenta previa (placenta covering the cervical os), low-lying placenta (edge located ≤20 mm from cervical os), or normally located placenta (edge located >20 mm from cervical os) (strong/moderate).
• 2Diagnosis of placenta previa or low-lying placenta should not be made <18 to 20 weeks gestation, and the provisional diagnosis must be confirmed after >32 weeks gestation, or earlier if the clinical situation warrants. In women with a low-lying placenta, a recent ultrasound (within 7 to 14 days) should be used to confirm placental location prior to a cesarean delivery (strong/moderate).
• 3Assessment by transvaginal ultrasound is recommended in all cases where placenta previa or a low-lying placenta is present or suspected by transabdominal sonography, with attempt to clearly define placental location (including laterality), characteristics of placental edge (including thickness, presence of a marginal sinus), and associated findings (succenturiate lobe, cord insertion close to the cervix) (strong/moderate).
• 4In women with placenta previa or low-lying placenta and in the presence of risk factors or limited access to urgent obstetrical care, consider in-hospital management (strong/moderate).
• 5A cervical cerclage can be considered in women with a short cervical length, particularly in association with antepartum hemorrhage, but not as a prophylactic measure for all women with placenta previa (conditional [weak]/low).
• 6Administer antenatal corticosteroids for potential preterm delivery only if the risk of delivery within 7 days is very high and not solely because admission to the hospital is deemed necessary (strong/moderate).
• 7Tocolysis can be considered in women with antepartum hemorrhage associated with uterine contractions in order to allow administration of corticosteroids or transfer of care, but not for prolongation of pregnancy (conditional [weak]/low).
• 8Cesarean delivery is recommended in women with placenta previa at 36⁰ to 36⁶ weeks gestation in the presence of risk factors and at 37⁰ to 37⁶ weeks gestation in the absence of risk factors (strong/moderate).
• 9Cesarean delivery is recommended in women with a low-lying placenta with the placental edge ≤10 mm from the cervical os at 37⁰ to 37⁶ weeks gestation in the presence of risk factors and at 38⁰ to 38⁶ weeks gestation in the absence of risk factors (strong/moderate).
• 10A trial of labour is recommended in women with a low-lying placenta where the placental edge is 11 to 20 mm from the cervical os and can be considered in carefully selected women where the placental edge is ≤10 mm from the cervical os (strong/moderate).

     

Clinical significances of magnetic resonance imaging in prenatal diagnosis of vasa previa in a woman with bilobed placentas

We report a case of a pregnant woman diagnosed as having vasa previa by magnetic resonance imaging (MRI). A parous woman was referred to our hospital at 31 weeks of gestation due to suspicion of placenta previa. Transvaginal ultrasound examination together with the Doppler techniques showed a fetal vessel on a lesion of low and high mixed echogenecities over the internal os, but could not confirm whether it was placental tissue or not. MRI demonstrated that it was not placenta but a hemorrhage between bilobed placentas and that the vessel was running over the internal os freely from the placenta. At 34 weeks of gestation, emergency cesarean section was performed due to increasing vaginal bleeding. MRI should be useful in the diagnosis of vasa previa when the relation between the position of the placenta and that of suspicious vessels cannot be adequately evaluated by ultrasound.