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Velamentous umbilical cord insertion and vasa previa

Authors: Charles J Lockwood, MD, MHCM, Karen Russo-Stieglitz, MDSection Editors: Lynn L Simpson, MD, Deborah Levine, MDDeputy Editor: Vanessa A Barss, MD, FACOG

All topics are updated as new evidence becomes available and our peer review process is complete.Literature review current through: May 2018. | This topic last updated: Mar 20, 2018.

INTRODUCTION — A velamentous umbilical cord is characterized by membranous umbilical vessels at theplacental insertion site; the remainder of the cord is usually normal. Membranous vessels can also arise asaberrant branches of a marginally inserted umbilical cord or they can connect lobes of a bilobed placenta orthe placenta and a succenturiate lobe. Because of the lack of protection from Wharton’s jelly, these vesselsare prone to compression and rupture, especially when they are located in the membranes covering thecervical os (ie, vasa previa).

VELAMENTOUS UMBILICAL CORD

Definition — In a velamentous umbilical cord insertion, the placental end of the cord consists of divergentumbilical vessels surrounded only by fetal membranes, with no Wharton's jelly. The length of themembranous vessels, ie, the distance between the end of the normal cord and the placental insertion, ishighly variable.

Prevalence — Velamentous insertion occurs in approximately 1 percent of singleton gestations [1], but isobserved in as many as 15 percent of monochorionic twin gestations [2-4]. It is also more common inplacenta previa than in normally located placentas. The prevalence may be slightly higher in stillbirths,particularly from multifetal pregnancies [4].

Pathogenesis — The pathogenesis of velamentous cord insertion is unknown. The most popular hypothesisis that the cord is initially inserted centrally, but its location progressively becomes peripheral as one half ofthe placenta actively proliferates toward the well-vascularized uterine fundus (trophotropism) while the otherpole involutes; the umbilical cord is unable to follow the migration of the placenta [5]. The association ofvelamentous cord insertion and placenta previa supports this hypothesis.

Clinical features

Ultrasound and gross examination — On ultrasound and gross examination, the normal umbilical cordsheath is contiguous with the chorionic plate. With a velamentous insertion, the cord can end severalcentimeters from the placenta, at which point the umbilical vessels separate from each other and crossbetween the amnion and chorion before connecting to the subchorionic vessels of the placenta (picture 1A-C). This typically occurs at the margin of the placenta (within 1 cm of the placental edge), but can also occurat the apex of the gestational sac. In monochorionic twins, the velamentous vessels often occur in thedividing membranes.

On ultrasound examination, the umbilical vessels often lie parallel to the uterine wall as they enter theplacental margin and connect to the subchorionic vasculature (image 1). They remain immobile when the

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uterus is shaken by the ultrasonographer; in contrast, a loop of umbilical cord will move when the uterus isshaken [6]. Color Doppler imaging enhances identification of the vessels (image 2).

Velamentous cords contain a single umbilical artery in about 12 percent of cases [5].

Clinical course — Because the vessels are attached to the chorion, rupture of the fetal membranes mayrupture the vessels, which can result in fetal exsanguination and death within minutes. This typically occurswhen the membranous vessels are close to or cover the cervix; rarely, membranous vessels have ruptured inthe absence of documented membrane rupture [7]. (See 'Vasa previa' below.)

The membranous vessels are also at risk of kinking and compression. Membranous vessels with longerlengths are more prone to kinking, while descent of the fetal presenting part increases the risk ofcompression when the membranous vessels are close to or cover the cervix. The subsequent reduction inblood flow can result in fetal heart rate abnormalities, and, if the reduction in blood flow is persistent orsevere, fetal death may occur. Kinking and compression can also induce thrombosis of the vessels, whichhas been associated with placental infarction, amputation of fetal limbs or digits, and neonatal purpura [8,9].

In a 2015 systematic review and meta-analysis that evaluated the association between placental implantationabnormalities and risk of preterm delivery in singleton gestations, velamentous cord insertions wereassociated with a high preterm delivery rate (37.5 percent) and increased perinatal risks, such as neonatalintensive care unit admissions, small for gestational age, and perinatal death [10]. The majority of includedstudies were descriptive, did not have a control group, and had small numbers of cases. However,subsequent larger studies have also reported an increased risk of adverse perinatal outcomes, includingdeath, although the absolute risk for these outcomes was low and was also low in the general population [11-13].

When only monochorionic twin pregnancies are examined, velamentous cord insertion site has beenassociated with discordant growth and intrauterine growth restriction [3,14].

The mother is also at risk for complications. A population-based series including over 11,000 pregnancieswith velamentous cord insertion noted 5.5 percent underwent manual removal of the placenta [15].

Diagnosis — The prenatal diagnosis of velamentous insertion is based upon the presence of characteristicsonographic findings (membranous umbilical vessels) at the placental cord insertion site. When color Doppleris used to enhance identification of the vessels, diagnostic sensitivities of 69 to 100 percent and specificitiesof 95 to 100 percent have been reported [1,16].

A definitive diagnosis is made by gross examination of the placenta, cord, and membranes after delivery(picture 1A-C). (See 'Ultrasound and gross examination' above.)

Screening — The American College of Radiology (ACR), the American Institute of Ultrasound in Medicine(AIUM), and the American College of Obstetricians and Gynecologists (ACOG) guideline for performance ofobstetric ultrasound does not specifically recommend evaluation of the placental insertion site [17]. Theguideline recommends that “the umbilical cord should be imaged, and the number of vessels in the cordshould be evaluated when possible” with evaluation of the “umbilical cord insertion site into the fetalabdomen.”

Most experts do not recommend routine screening for velamentous insertion, as it is costly in low riskpatients with no proven benefit while increasing anxiety and possibly unnecessary antepartum testing andintervention. However, some authors have opined that every second trimester ultrasound examination orevery second trimester ultrasound in monochorionic twin pregnancies should evaluate the placental cordinsertion. Even when this is done, the diagnosis of velamentous insertion may not be made in the prenatalperiod, and failure to make this diagnosis is not a breach of the standard of care [18].

Management — There are no data from large or controlled studies on which to base managementrecommendations. There is no evidence that interventions such as late preterm induction of labor or

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scheduled cesarean delivery improve outcome. In our opinion, these pregnancies can be allowed to laborspontaneously and deliver vaginally, in the absence of additional pregnancy complications necessitating adifferent approach. However, we do not allow these pregnancies to continue beyond 40 weeks of gestationsince decreasing amniotic fluid volume postterm may place the membranous vessels at increased risk ofcompression.

Given the risks described above, if ultrasound examination suggests the presence of a velamentous umbilicalcord, we suggest the following:

We monitor the fetal heart rate continuously intrapartum to identify signs of severe cord compression orvessel rupture. After delivery of the infant, no or very gentle traction should be placed on the umbilical cord toavoid avulsion, which could result in a retained placenta.

VASA PREVIA

Definition — In vasa previa, fetal blood vessels are present in the membranes covering the internal cervicalos. The membranous vessels may be associated with a velamentous umbilical cord (type 1 vasa previa) orthey may connect the lobes of a bilobed placenta or the placenta and a succenturiate lobe (type 2 vasaprevia) [19].

Aberrant blood vessels within 2 cm of the internal os have similar implications to those actually covering theinternal os [20-23]. While there is a conventional threshold of 2 cm from the internal os to the vessel used todefine vasa previa, the exact distance presenting an increased risk has not been determined.

Prevalence — The prevalence of vasa previa is approximately 1 in 2500 deliveries [21,24], but is muchhigher in pregnancies conceived following use of assisted reproductive technologies (prevalence as high as 1in 202) [25-28]. The prevalence is also increased in second-trimester low-lying placentas or placenta previa(even if resolved), bilobed or succenturiate lobe placentas in the lower uterine segment, and multiplegestations [27,29].

Pathogenesis — Pathogenesis is unknown, but is likely similar to that for velamentous cord insertion.Resolution of placenta previa or low-lying placenta may result in type I vasa previa. (See 'Pathogenesis'above.)

Risk factors — Risk factors for vasa previa are not independent and include velamentous cord insertion,umbilical cord insertion in the lower part of the uterus at first-trimester ultrasound, placenta previa or low-lyingplacenta on second-trimester ultrasound scan, succenturiate placental lobe or bilobed placenta, in vitrofertilization, and multiple gestation [30-32]. The placental location and the relationship between the placentaand internal cervical os should be evaluated carefully in these patients.

A systematic review of predictive indicators of vasa previa found at least 83 percent of cases had one ormore risk indicators, most commonly placenta previa, assisted conception, velamentous cord insertion, andbilobed placenta [33].

Clinical features

Detailed fetal anatomic survey, including evaluation for coexistent vasa previa●

Serial assessment of fetal growth, every four to six weeks●

Fetal heart rate tracings weekly, beginning at 36 weeks of gestation, to look for recurrent variabledecelerations from kinking or compression

●

Counseling patients to call their providers as soon as labor begins●

Delivery by 40 weeks of gestation●












Imaging — On ultrasound examination, vasa previa appears as a linear sonolucent area that passes overthe internal os. Color Doppler flow mapping showing umbilical artery or vein waveforms confirms that thesonolucency is a blood vessel (image 3).

In one review, the placenta was a previa, low-lying, bilobed, or succenturiate in about 90 percent of cases[34]. In a retrospective single center study, the cord insertion was velamentous or marginal or the placentawas a previa or low lying in 95 percent of cases [21]. If the placenta is a previa or low lying, the umbilical cordinsertion site is velamentous.

Physical examination — Rarely, pulsating vessels in the membranes overlying the cervical os arepalpable on digital examination.

Clinical course — Suspected second trimester vasa previa may resolve over time. In one series, 3 of 18cases resolved by the late third trimester and had an uncomplicated vaginal delivery; diagnosis was based onaberrant vessels over the internal os [20]. In a second series, 5 of 21 cases diagnosed in the secondtrimester resolved, while none of 8 cases diagnosed in the third trimester resolved; vasa previa was definedas a fetal vessel within 2 cm of the internal cervical os on transvaginal sonography [22]. In a third series, 5 of56 cases resolved by delivery and were considered false positive diagnoses due to a loop of cord or dilatedmaternal vessels in the lower uterus [21]. (See 'Differential diagnosis' below.)

More commonly, the vasa previa persists and is at risk for rupture upon spontaneous or artificial rupture ofthe membranes; rarely, fetal bleeding occurs without membrane rupture. In most cases, bleeding rapidlyresults in hypotension, leading to fetal heart rate abnormalities, such as a sinusoidal pattern; fetal death dueto exsanguination can occur within minutes. In two series, 50 to 60 percent of pregnancies were deliveredelectively, and the remainder were delivered emergently primarily because of contractions or labor, bleeding,nonreassuring fetal heart rate tracing, or other (eg, asymptomatic cervical shortening, preeclampsia) [21,35].In one of these series, the likelihood of delivery in the next week increased substantially at 34 to 35 weeks[21].

Perinatal mortality rates are low (less than 10 percent) with antepartum diagnosis and appropriatemanagement, and obviously higher among pregnancies diagnosed intrapartum or postpartum as a result offetal complications [32,36]. In monochorionic twin gestations, the perinatal mortality rate is high for bothtwins, even if the vasa previa is associated with only one twin, due to the presence of placental vascularanastomoses [37].

As with velamentous cord insertion, the membranous vessels are at risk of compression from the fetalpresenting part since they are not protected by the structure of a normal umbilical cord. Compression couldlead to fetal asphyxia.

In one study, type 1 vasa previa was associated with lower mean birth weight than type 2 vasa previa (2494versus 3037 grams), and lower placental weight [38]. The authors hypothesized that growth inhibition wasdue to a combination of a primary placental developmental disorder and alterations of the umbilical circulationin the velamentous cord.

Pathology — Pathological examination may reveal membranous vessels, but otherwise is not usefulsince the pathologist cannot determine the location of the placenta and cord in the uterus.

Diagnosis — Prenatal diagnosis of vasa previa is based on identification of membranous fetal vesselspassing across or in close proximity to the internal cervical os by real-time transvaginal ultrasoundexamination with color Doppler (image 3) (see 'Imaging' above). Close proximity has been defined as within 2cm of the internal os; however, only limited data are available to support this specific measurement [22]. Inprospective studies in which the investigators were specifically looking for vasa previa, sonography plus colorDoppler had high diagnostic sensitivity: 10/10 cases after 26 weeks [19] and 1/1 case at 18 to 20 weeks [39];in each study, one additional case diagnosed prenatally could not be confirmed at delivery. In a systematicreview including both prospective and retrospective studies, sensitivity ranged from 53 to 100 percent [40].





















Magnetic resonance imaging can be used to clarify the ultrasound diagnosis if there is diagnostic uncertaintyand confirmation will affect pregnancy management [23,41-43].

Several case reports have described use of three-dimensional (3D) ultrasound technology for the diagnosisof vasa previa and to determine the optimum site for hysterotomy at delivery [44-47]. Although technicallyfeasible, use of 3D technology has not been proven superior to two-dimensional (2D) technology, as arterialand venous color flow mapping can be easily performed with 2D technology alone. In addition, 3D technologyis not universally available.

In the absence of prenatal sonographic diagnosis, a clinical diagnosis of vasa previa should be suspected inthe setting of vaginal bleeding that occurs upon rupture of the membranes and is accompanied by fetal heartrate abnormalities, particularly a sinusoidal pattern or bradycardia. Confirmation that the blood is fetal via Apt,Kleihauer-Betke tests, or other tests (Ogita, Londersloot) supports the diagnosis [48]; however, there isusually no time to wait for test results before performing an emergency cesarean delivery for fetal distress.

Differential diagnosis

Funic presentation — A loop of umbilical cord lying over the cervical os can be mistaken for vasa previa.In contrast to vasa previa, the umbilical vessels in funic presentation are surrounded by Wharton’s jelly andcan float away from the cervical os if the uterus is shaken or the patient is placed in knee-chest orTrendelenburg position. We suggest using the abdominal hand to push the presenting part cephalad in anattempt to better visualize the area of the internal os when the presenting part is engaged. This will helpdistinguish between a vasa previa and a funic presentation.

Cervico-uterine vessels — In vasa previa, pulsed Doppler will demonstrate a rate consistent with thefetal heart rate and thus distinguish blood flowing in fetal vessels from maternal blood flowing in cervicalarteries or a marginal utero-placental vascular sinus.

Cervical varicosities are rare in pregnancy [49-51]. Like vasa previa, cervical varices can appear assonolucent tubules in the area of the internal os with blood flow on Doppler imaging. However, the tubules donot pass across the os, are tortuous, and may be part of a venous plexus.

Amniotic band or chorioamniotic separation — An amniotic band or chorioamniotic separation maycreate the appearance of a sonolucent structure crossing the cervical os; however, color Doppler will notdemonstrate blood flow, thereby excluding the diagnosis of vasa previa.

Screening — Women with placenta previa (even if resolved) or a low lying placenta on midtrimesterultrasound examination should undergo transvaginal ultrasound with color and pulsed Doppler at 32 weeks ofgestation to screen for vasa previa [30].

The benefits of antenatal diagnosis and targeted management were illustrated by a series that reportedneonatal survival in 59 of 61 cases (97 percent) suspected antenatally, but only 41 of 94 cases (44 percent)without prenatally suspected diagnosis [52]. Surviving infants without prenatally suspected diagnosis hadlower Apgar scores (mean five-minute Apgar score of 4 versus 9) and required more blood transfusions (59versus 3 percent). The mean gestational age at delivery of survivors and non-survivors was 36.5 and 37.6weeks, respectively, and mean gestational age at delivery in those with and without prenatal diagnosis was34.9 and 38.2 weeks, respectively. However, these results may be biased since most of the data came fromwomen who chose to register with the Vasa Previa Foundation's web site.

A decision-analytic model to estimate the lifetime incremental costs and benefits of screening for vasa previaconcluded that universal transvaginal ultrasound screening of twin pregnancies had an incremental cost-effectiveness ratio (ICER) of $5488 per quality-adjusted life-years (QALY)-gained [53]. For singletonpregnancies with risk factors including low-lying placentas, pregnancy following in vitro fertilization, accessoryplacental lobes, or velamentous cord insertion, the ICER was $15,764 per QALY-gained. In contrast,


https://www.uptodate.com/contents/velamentous-umbilical-cord-insertion-and-vasa-previa/abstract/23,41-43










universal transvaginal screening for vasa previa in singleton pregnancies was not cost effective ($579,164per QALY).

Management — There are no high-quality data on which to base recommendations for optimal timing ofantenatal corticosteroid administration, antenatal fetal monitoring, hospitalization, and scheduled delivery.Our recommendations, and those of others, are based on data from retrospective case series.

Antepartum — If vasa previa is identified on prenatal ultrasound examination, we begin weekly nonstresstesting on outpatients at 32 weeks of gestation to look for any evidence of cord compression. In a series of 68pregnancies with vasa previa undergoing nonstress testing in inpatient and outpatient settings, outpatientnonstress testing led to earlier hospitalization in several cases but did not affect the timing of delivery [32].

Because of the increased risk of emergency preterm delivery in the third trimester, we suggest administrationof a course of betamethasone between 28 and 32 weeks of gestation and hospital admission between 30and 34 weeks of gestation. Hospitalization allows for close surveillance for signs of cord compression. Weperform nonstress tests two to three times daily on our inpatients. In a series including 21 women with vasaprevia managed as outpatients, 15 women (71 percent) required admission due to various complications, and47 percent of these women required emergency cesarean [54]. Emergency cesarean delivery can beperformed promptly if cord compression or early labor is detected, ideally before rupture of membranes.

Ambulatory monitoring is also a reasonable option, particularly in women with a long closed cervix, nocontractions or vaginal bleeding, no history of spontaneous preterm birth, and who live close to the hospital.Since cervical shortening maybe predictive of the onset of labor, some authors have suggested using cervicallength measurements to help with individualized decision-making regarding safety of outpatient managementand timing of delivery; however, this approach has not been validated [32,55,56].

Case reports have described use of fetoscopic laser ablation for treatment of type 2 vasa previa, with variableoutcomes [57,58]. This procedure should be considered investigational.

Delivery — We deliver the fetus by emergency cesarean delivery if any of the following occur:

We agree with the authors of a decision analysis [59] who recommended delivery at 34 to 35 weeks ofgestation, without assessment of fetal lung maturity [59]. Delivery at this gestational age achieved balancebetween the risk of perinatal death and the risks of mortality and morbidity related to prematurity. The Societyfor Maternal-Fetal Medicine Consult Series concluded planned cesarean delivery because of vasa previa isreasonable at 34 to 37 weeks of gestation [30,60]. The Obstetrix Collaborative Research Networkrecommended elective delivery at 33 to 34 weeks gestation [32].

There is no clear evidence to recommend a different approach in twin pregnancies with vasa previa. Earlierscheduled delivery at 32 or 33 weeks is reasonable if imminent delivery seems likely because of a shortcervix or threatened preterm labor. In two series, the median gestational age at delivery for twin pregnancieswith vasa previa was 32 to 33 weeks of gestation [21,35].

Type O negative blood should be available for emergency transfusion of a severely anemic newborn, whenclinically indicated.

Ideally, the hysterotomy should avoid aberrant blood vessels. If a fetal vessel is lacerated inadvertently duringdelivery, the cord should be clamped immediately to prevent fetal/neonatal blood loss [30].

Labor●

Premature rupture of membranes●

Repetitive variable decelerations refractory to tocolysis●

Vaginal bleeding accompanied by fetal tachycardia, a sinusoidal heart rate pattern, or evidence of purefetal blood by Apt test or Kleihauer-Betke assessment

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SUMMARY AND RECOMMENDATIONS

Velamentous umbilical cord:

Vasa previa:

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REFERENCES

1. Sepulveda W, Rojas I, Robert JA, et al. Prenatal detection of velamentous insertion of the umbilicalcord: a prospective color Doppler ultrasound study. Ultrasound Obstet Gynecol 2003; 21:564.

The prenatal diagnosis of velamentous cord insertion is based upon the presence of characteristicsonographic findings (splayed, membranous umbilical vessels with no Wharton's jelly) at the placentalumbilical cord insertion site. A definitive diagnosis of velamentous cord insertion is made by pathologicexamination of the placenta, cord, and membranes after delivery. (See 'Ultrasound and grossexamination' above and 'Diagnosis' above.)

●

The vessels in a velamentous umbilical cord are at increased risk of compression compared to a normalcord. We suggest fetal heart rate monitoring to detect compression of cord vessels beginning at 36weeks of gestation. (See 'Management' above.)

●

There is no evidence that induction of labor or scheduled cesarean delivery improve the outcome ofpregnancies complicated by velamentous cord insertion without vasa previa. We continuously monitorthe fetal heart rate during labor and exercise caution when exerting traction on the umbilical cord afterbirth. (See 'Management' above.)

●

The prenatal diagnosis of vasa previa is based upon characteristic sonographic findings (membranousvessels that cross the internal cervical os). In the absence of prenatal sonographic diagnosis, a clinicaldiagnosis of vasa previa should be suspected in the setting of vaginal bleeding that occurs upon ruptureof the membranes and is accompanied by fetal heart rate abnormalities, particularly a sinusoidal patternor bradycardia. Fetal exsanguination can occur within minutes. (See 'Imaging' above and 'Clinical course'above and 'Diagnosis' above.)

●

Risk factors for vasa previa are not independent and include velamentous cord insertion, umbilical cordinsertion in the lower part of the uterus at first-trimester ultrasound, placenta previa or low-lying placentaon second-trimester ultrasound scan, succenturiate placental lobe or bilobed placenta, in vitrofertilization, and multiple gestation. The placental location and the relationship between the placenta andinternal cervical os should be evaluated carefully in these patients. (See 'Risk factors' above.)

●

Women with placenta previa (even if resolved) or a low lying placenta on midtrimester ultrasoundexamination should undergo transvaginal ultrasound with color and pulsed Doppler at 32 weeks ofgestation to screen for vasa previa. (See 'Screening' above.)

●

The frequency and severity of cord compression may be higher for vasa previa than velamentousumbilical cord (without vasa previa); therefore, we monitor pregnancies with vasa previa more closely.We suggest administration of a course of betamethasone at 28 to 32 weeks, weekly nonstress testingbeginning at 32 weeks in outpatients, with hospitalization at 30 to 34 weeks of gestation for morefrequent monitoring to detect early evidence of cord compression. Hospitalization also facilitates theability to perform an emergency cesarean delivery in the event of premature rupture of membranes orpreterm labor. (See 'Antepartum' above.)

●

For pregnancies with vasa previa, we suggest scheduled delivery at 34 to 35 weeks of gestation (Grade2C). (See 'Delivery' above.)

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GRAPHICS

Velamentous cord

The umbilical cord placental insertion site is membranous. The velamentousvessels are surrounded only by fetal membranes, with no Wharton's jelly.

Courtesy of Eduardo Zambrano, MD, MS.

Graphic 50561 Version 2.0





Velamentous cord

Velamentous umbilical cord insertion of a bilobed placenta.

Courtesy of the Pathology Department at The Valley Hospital in Ridgewood,New Jersey.






Velamentous cord insertion

Diamnionic, monochorionic twin placenta with the intervening amnion rolled in thecenter. Notice the haphazard vascularization (large arrow). The velamentous cordinsertion (small arrow) of the smaller twin of this discordant pair is not an unusualfinding in monochorionic twins.

Reproduced with permission from: Mhairi G. MacDonald, Mary M. K. Seshia, et al.Avery's Neonatology Pathophysiology & Management of the Newborn, 6th Edition.Philadelphia: Lippincott Williams & Wilkins, 2005. Copyright © 2005 LippincottWilliams & Wilkins.






Ultrasound image of velamentous umbilical cord

Grey scale image of umbilical cord (arrow) inserting into the fetal membranes, awayfrom the placenta (P).

Courtesy of Deborah Levine, MD.






Color Doppler image of velamentous umbilical cord

Color Doppler shows flow in the umbilical vessels separate from the cord andextending to the placenta.

Courtesy of Deborah Levine, MD.






Ultrasound images of vasa previa

Transvaginal ultrasound images showing a posterior placenta with an anteriorsuccinturiate lobe complicated by vasa previa.

Courtesy of The Division of Maternal Fetal Medicine at The Valley Hospital, RidgewoodNew Jersey.






Contributor Disclosures

Charles J Lockwood, MD, MHCM Nothing to disclose Karen Russo-Stieglitz, MD Nothing todisclose Lynn L Simpson, MD Nothing to disclose Deborah Levine, MD Nothing to disclose Vanessa ABarss, MD, FACOG Nothing to disclose

Contributor disclosures are reviewed for conflicts of interest by the editorial group. When found, these areaddressed by vetting through a multi-level review process, and through requirements for references to beprovided to support the content. Appropriately referenced content is required of all authors and must conformto UpToDate standards of evidence.

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