Case Report

Vasa Previa: Prenatal Diagnosis byTransperineal Sonography withDoppler Evaluation

Barbara S. Hertzberg, MD, Mark A. Kliewer, MD

Department of Radiology, Box 3808, Room 24244B, Red Zone South, Duke University Medical Center,Durham, North Carolina 27710

Received 2 February 1998; accepted 8 April 1998

ABSTRACT: Antepartum diagnosis of vasa previa is ofcritical importance because of the high fetal mortalityrate in unrecognized cases. This report describes thesonographic findings in 2 cases of vasa previa anddemonstrates that transperineal sonography withDoppler evaluation can successfully establish the di-agnosis of vasa previa prenatally. © 1998 John Wiley& Sons, Inc. J Clin Ultrasound 26:405–408, 1998.

Keywords: placenta, abnormalities; pregnancy, ultra-sonography; placenta, ultrasonography

Vasa previa results when placental blood ves-sels traverse the internal cervical os without

the protective covering of the placenta or umbili-cal cord. Because this anomaly carries one of thehighest fetal mortality rates of any complicationof pregnancy,1,2 accurate prenatal diagnosis iscritical. However, vasa previa frequently remainsunrecognized until the onset of complications. An-tepartum identification of vasa previa has beendescribed using transabdominal and endovaginalsonography supplemented by Doppler evalua-tion.3–13 Although many laboratories image thecervix and assess placental location using a trans-perineal approach, to our knowledge the diagno-sis of vasa previa by transperineal sonographyhas not been previously reported. This report de-scribes the sonographic findings in 2 cases inwhich the diagnosis of vasa previa was estab-lished prenatally using transperineal sonographywith Doppler evaluation.

CASE REPORTS

Case 1

A 22-year-old white woman with a history of aprior twin pregnancy delivered by cesarean sec-tion first presented for prenatal care in the thirdtrimester of pregnancy. The current pregnancywas uncomplicated, and the patient was referredfor sonographic examination to evaluate fetalanatomy and to estimate gestational age. Sonog-raphy revealed an intrauterine pregnancy with asingle live fetus of an estimated gestational age of30 weeks 2 days. Fetal anatomy appeared normal.The placenta had anterior and posterior lobes(Figure 1A). The cervix was not optimally seenfrom the transabdominal perspective, so imagesfrom the transperineal perspective were obtained.These revealed blood vessels extending betweenthe anterior and posterior lobes of the placentaand crossing over the cervix, consistent with vasaprevia (Figures 1B and 1C). Follow-up sono-graphic examination performed at a gestationalage of 34 weeks 1 day confirmed these findingsand showed appropriate interval growth.

The patient presented with vaginal bleeding at35 weeks’ gestational age. Amniocentesis to de-termine the lecithin-sphingomyelin ratio con-firmed fetal lung maturity, and the patient un-derwent cesarean section. Vasa previa and asuccenturiate lobe of the placenta were confirmedat the time of cesarean section. After manual re-moval of the placenta, there was brisk hemor-rhage from the lower uterine segment, necessitat-ing cesarean hysterectomy. Pathologic evaluationof the surgical specimen further confirmed a suc-

Correspondence to: B. S. Hertzberg

© 1998 John Wiley & Sons, Inc. CCC 0091-2751/98/080405-04

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centuriate lobe of the placenta and vasa previaand revealed no evidence of placenta accreta.

Case 2

A 33-year-old pregnant black woman, gravida 4para 3, was referred for sonographic examinationbecause a serum a-fetoprotein screening test in-dicated an elevated risk for Down syndrome. Thecurrent pregnancy was otherwise uncomplicated.She had had 3 prior spontaneous vaginal deliver-ies at term.

Sonography revealed a single intrauterine fe-tus with an estimated gestational age of 16

weeks. Fetal anatomy was normal, and a poste-rior placental lobe with marginal placenta previawas seen. After genetic counseling, the patientdeclined amniocentesis. Follow-up sonographicexaminations at 24, 29, and 34 weeks’ gestationalage confirmed the marginal placenta previa andrevealed appropriate interval growth. Two pla-cental lobes, 1 along the anterior and the otheralong the posterior surface of the uterus, wereidentified at 34 weeks. Although the anterior pla-cental lobe had not been perceived as a discreteaccessory lobe at the time of the previous sono-graphic examinations, review of the sonogramsrevealed that discrete anterior and posterior lobes

FIGURE 1. Sonograms from a patient with succenturiate placental lobes and vasa previa (case 1) obtained at a gestational age of 30 weeks 2 days.(A) Longitudinal transabdominal sonogram depicts anterior (A) and posterior (P) placental lobes. (B) Transperineal color Doppler sonogram ofthe cervix (C) and lower uterus reveals blood vessels (arrow) bridging the anterior (A) and posterior (P) lobes of the placenta, consistent withvasa previa. (C) Spectral Doppler sampling of blood vessels overlying the cervix in B reveals arterial (straight arrow) and venous (curved arrow)flow.

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had likely been present. Transperineal sonogra-phy with color Doppler evaluation revealed ablood vessel bridging the two lobes of the placentaand crossing over the internal cervical os, consis-tent with vasa previa.

Because of the suspected vasa previa, amnio-centesis for lung maturity was performed at 1-week intervals. Lung maturity was documentedat 37 weeks’ gestational age, and the patient un-derwent elective cesarean section. A succenturi-ate lobe of the placenta was confirmed at cesareansection, with a placental vessel extending fromthe main posterior placental lobe across the cer-vix and into the anterior succenturiate lobe, con-sistent with vasa previa. A small portion of theposterior placental tissue was densely adherentto the uterus and required blunt dissection forremoval. Pathologic analysis confirmed the suc-centuriate lobe of the placenta, with focal pla-centa accreta of the main placental lobe. The pa-tient did well after delivery and had a normal6-week postpartum follow-up clinic visit.

DISCUSSION

When there is a velamentous insertion of the um-bilical cord or a succenturiate or bilobate pla-centa, placental vessels will occasionally travelwithin the membranes without the protective cov-ering of the placenta or umbilical cord and willcross the internal cervical os in advance of thepresenting part of the fetus. These exposed bloodvessels are vulnerable to injury and bleeding atthe time of membrane rupture. In the event ofbleeding, rapid fetal exsanguination and deathcan ensue. The bleeding comes from the fetusonly; oddly, there is little or no risk to themother.1,2 Even in the absence of bleeding, com-pression of the blood vessels by the presentingpart of the fetus against the bony pelvis can leadto hypoxia and fetal death.1,2 Albeit a relativelyuncommon complication,1,14,15 vasa previa is anabsolute indication for cesarean section and a po-tentially lethal diagnosis to miss.

Despite its importance, the prenatal diagnosisof vasa previa can be difficult and is oftenmissed.1,2,14,15 Before sonography, the methods ofdiagnosis of vasa previa were limited. They in-cluded direct visualization and palpation of theoffending blood vessels, fetal heart rate monitor-ing, amnioscopy, and blood sample analysis forpurely fetal blood components.1 Unfortunately,diagnostic techniques such as amnioscopy and di-rect visualization and palpation can themselvesprecipitate vessel rupture and fetal hemor-rhage.13 Further, the clinical presentation of

third-trimester vaginal bleeding can cause vasaprevia to be presumptively misdiagnosed as pla-centa previa or abruptio placentae. The applica-tion of sonography to this difficult diagnosis hasbeen lauded with understandable enthusiasm.

Prenatal sonographic diagnosis depends on ahigh level of suspicion in the appropriate setting.Vasa previa should be specifically sought whenthere is a succenturiate or bilobate placenta im-planted low in the uterus or a low velamentousinsertion of the umbilical cord. Vasa previa can bediagnosed if curvilinear or tubular vascular struc-tures overlie the internal cervical os.6,7,12 Supple-menting gray-scale sonography with color Dopp-ler sonography and/or spectral analysis enablesconfirmation of the vascular nature of the struc-tures and thereby increases the level of confi-dence in the diagnosis.3–5,8–11,13,16 Color Dopplerimaging might also enable identification ofsmaller vessels that could be overlooked usinggray-scale imaging alone.11

The current literature on the sonographic di-agnosis of vasa previa is largely composed of re-ports in which this diagnosis was made withtransabdominal or endovaginal sonography andis pointedly lacking in prospective series. Trans-abdominal sonography can be diagnostic for vasaprevia when the cervix is directly visualized, butthe cervix may be obscured from this perspectiveby the presenting part of the fetus, particularly inthe third trimester.17,18 Not surprisingly, an in-creasing number of cases have been diagnosed us-ing endovaginal sonography.4,5,9,10,16 Althoughendovaginal sonography can be safely performedin patients with vasa previa,4,5,9–11,16,19,20 itshould be done cautiously to minimize manipula-tion of the cervix and thereby to decrease thetheoretical risk of inducing bleeding.

Transperineal sonography provides an alterna-tive and complementary perspective for imagingthe cervix that does not require vaginal penetra-tion. This technique is used in many clinics tovisualize the cervix and to assess placental loca-tion.17,18,21,22 The cases reported here confirmthat transperineal sonography can successfullyvisualize blood vessels crossing the cervical os incases of vasa previa. Confirmation that the struc-tures crossing the os are blood vessels can be ob-tained with Doppler evaluation in this transperi-neal perspective.

Vasa previa is sufficiently rare that routineDoppler evaluation of the cervical region hardlyseems warranted for all pregnant patients. In-stead, these efforts should be reserved for pa-tients at significantly increased risk for vasa pre-via, ie, those who have a succenturiate or bilobate

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placenta or a velamentous umbilical cord inser-tion. In such cases, cervical imaging supple-mented with color Doppler interrogation for bloodvessels overlying the cervix can be accomplishedby transabdominal, endovaginal, or, as this reportshows, transperineal sonography. The transperi-neal perspective can provide high-quality gray-scale and Doppler sonograms of vasa previa an-tepartum.

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