Obstetrics and Gynecology

Vasa previa

Vasa previa (Benckiser's hemorrhage)

1. What every clinician needs to know

Clinical features and incidence

Vasa previa is a condition where fetal vessels, unprotected by umbilical cord or placental tissue, run through the membranes over the cervix and below the presenting fetal part (Figure 1). Artificial or spontaneous rupture of the membranes often leads to rupture of these vessels and consequent fetal exsanguination and death. Unfortunately, this condition is often not diagnosed prior to fetal death. Thus it is associated with a very high perinatal mortality. The key to a good outcome lies in making the diagnosis prenatally and cesarean delivery before the membranes rupture. Ultrasound can diagnose vasa previa, and its liberal use in looking for vasa previa may prevent perinatal deaths from vasa previa.

Figure 1.

Photo of placenta after delivery showing vasa previa. The cord (clamped) is seen ending in the membranes through which fetal vessels run before inserting into the placenta.

Vasa previa typically presents with painless bleeding at the time of rupture of the membranes, followed by rapid fetal exsanguination and death. The condition may also present with fetal heart rate variable decelerations. In cases in which fetal blood loss has occurred, there may be a sinusoidal fetal heart rate pattern. While the actual incidence is extremely difficult to estimate, it appears that vasa previa complicates approximately 1 in 2,500 births. The true incidence is unknown because the majority of cases of vasa previa may not be recognized. For instance, some unexplained stillbirths may be due to vasa previa. Without close examination of the placenta, it may never be known that the demise resulted from a ruptured vasa previa.

Risk factors

The most important risk factor for vasa previa is a low-lying placenta or placenta previa in the second trimester. At least two-thirds of women who develop a vasa previa would have previously had a second trimester placenta previa; in the majority of cases, this placenta previa would have resolved by the time of delivery, leaving behind a vasa previa. Other risk factors include pregnancies resulting from in vitro fertilization, multi-fetal pregnancies, and those with bi-lobed or succenturiate lobed placentas. In these patients, ultrasound should be performed to look for vasa previa.

2. Diagnosis and differential diagnosis

Establishing the diagnosis

Vasa previa typically is diagnosed in one of two main ways: First, the condition may be diagnosed following fetal death after painless vaginal bleeding that occurred when the membranes ruptured. Examination of the placenta showing ruptured vessels running freely through the membranes confirms the diagnosis. The second method of diagnosis is through the use of prenatal ultrasound that demonstrates fetal vessels running over the cervix (see below). The keys to prenatal diagnosis are a high index of suspicion and a targeted examination for vasa previa, especially in those pregnancies that are at risk - i.e. those with second trimester low-lying placentas, bi-lobed or succenturiate lobed placentas, pregnancies resulting from in vitro fertilization and multi-fetal pregnancies.

More rarely, vasa previa may be diagnosed when a digital vaginal examination is done on a patient with a dilated cervix and intact membranes, as may occur during labor. Sometimes vessels can be palpated running through the intact amniotic forebag. These vessels have been described as feeling "cord-like". In some cases, a fetal pulse may be palpated.

Amnioscopy may visualize fetal vessels in the membranes, but this technique is no longer widely used.

Ultrasound findings

It is important, as part of routine prenatal sonography, to document the umbilical cord insertion into the placenta. If this is found to be normal, vasa previa is highly unlikely unless the placenta has an accessory lobe. Ultrasound of the region overlying the cervix also should be performed to look for evidence of vasa previa. Whenever there is a suspicion for vasa previa or when risk factors for the condition exist, transvaginal sonography with Doppler should be performed.

The fetal vessels appear as hypoechoic linear structures overlying the cervix (Figure 2). When color or power Doppler are used, flow through these structures will be demonstrated (Figure 3). Pulsed wave Doppler that reveals a fetal umbilical arterial or venous waveform with a fetal heart rate confirms the diagnosis. Thus ultrasound is the main test for diagnosing a vasa previa.

Figure 2.

Gray scale transvaginal sonogram showing linear hypoechoic structures overlying the cervix (c), representing a vasa previa. The fetal head = h.

Figure 3.

Vasa previa. Color Doppler demonstrating a fetal vessel running over the cervix (c). The fetal head = h.

Testing for fetal blood in vaginal blood may help diagnose a bleeding vasa previa. Bedside tests such as the Apt or Ogita tests have been used in the past. However, due to medical institution regulations, these tests are no longer widely available in the US.

Differential diagnosis

The differential diagnoses include other causes of bleeding during pregnancy such as placenta previa and placental abruption. When ultrasound is suggestive of vasa previa, a differential diagnosis is a funic presentation (loops of umbilical cord lying over the cervix). However, a vasa previa will remain in the same location on repeated examinations and the vessels will not move with movement of the patient, while a funic presentation will change position on repeated examinations or with movement of the patient.

Other differential diagnoses on ultrasound include movement artifact, which could lead to Doppler flow on ultrasound. Maternal vessels in the cervix or placenta also may also be mistaken for a vasa previa. It is important to use pulsed wave Doppler to demonstrate a fetal arterial or venous waveform; this will confirm that these are fetal vessels. To accurately make the diagnosis, transvaginal ultrasound should be performed with color, power and pulsed wave Doppler.

3. Management

Antepartum

The patient should be monitored closely for preterm labor, bleeding or rupture of membranes. Steroids should be administered at about 32 weeks. Hospitalization at 32 weeks is reasonable to allow proximity to the operating room and emergency cesarean should the membranes rupture. Fetal growth ultrasounds should be performed at least every 4 weeks. Cervical length evaluations may help in assessing the patient's risk for preterm delivery or rupture of the membranes.

An alternative to hospitalization at 32 weeks is outpatient management. This should only be done if the patient has no symptoms of preterm labor or bleeding, has a long closed cervix on transvaginal ultrasound, a negative fetal fibronectin test and no prior history of spontaneous preterm delivery. The patient should be admitted to a hospital with adequate specialist neonatal facilities.

Intrapartum

The patient should not be allowed to labor. She should be delivered by elective cesarean at about 35 weeks. Delaying delivery until after 36 weeks increases the risk of membrane rupture. Care should be taken to avoid incising the fetal vessels at the time of cesarean delivery. If vasa previa is recognized during labor in an undiagnosed patient, she should be delivered by urgent cesarean. The placenta should be examined to confirm the diagnosis.

Postpartum

Routine postpartum management as for cesarean delivery. If the fetus is born after blood loss, transfusion of blood without delay may be life-saving. It is important to have O negative blood or type-specific blood available immediately for neonatal transfusion.

4. Complications

Fetal demise may occur if the membranes and the fetal vessels rupture. Also, the fetus may lose considerable blood and may suffer hypovolemic shock, which may result in long term neurodevelopmental handicap. Pressure on the vessels by the presenting part may lead to intrauterine growth restriction. The key to reducing these risks lies in making the diagnosis prenatally and delivering the patient by elective cesarean prior to rupture of the membranes. Serial growth ultrasounds should be performed approximately every 4 weeks.

5. Prognosis and outcome

A. Fetal/neonatal outcomes

The outcome with vasa previa depends almost entirely on whether or not the condition is diagnosed prenatally and whether or not the patient is delivered by cesarean prior to the rupture of membranes. When the diagnosis is not made prenatally, the mortality rate is approximately 44%. When diagnosed prenatally and delivered by cesarean prior to rupture of the membranes, survival of the fetus approaches 100%.

When the membranes rupture prior to delivery, there is a high chance of fetal or neonatal death. Survivors in this situation are likely to require blood transfusions and may suffer from hypoxic-ischemic encephalopathy with long term handicap.The median Apgar scores for these survivors are 1 at 1 minute and 4 at 5 minutes, respectively. In cases where the diagnosis is made prenatally and the fetus delivered by elective cesarean, neonatal outcomes are excellent. Perhaps the biggest risk is that of prematurity.

B. Impact on mother's long-term health

Apart from the usual risks of cesarean delivery, vasa previa should not have any long term impact on the health of the patient. However, when the fetus loses significant blood, long term consequences may include neurodevelopmental handicap.

6. What is the evidence for specific management and treatment recommendations

Oyelese, Y, Catanzarite, V, Prefumo, F, Lashley, S, Goldstein, V. "Vasa previa: the impact of prenatal diagnosis on outcomes". Obstet Gynecol May. vol. 103. 2004. pp. 937-42.

(This study of 155 cases of vasa previa aimed at determining factors that led to survival in vasa previa. The study compared outcomes in cases diagnosed prenatally with those not diagnosed prenatally. The authors found that in the prenatally diagnosed cases, the perinatal survival was 97%, compared with only 44% when the diagnosis was not made prenatally. Also median 1 and 5 minute Apgar scores were 8 and 9 among the prenatally diagnosed group, compared with 1 and 4 in those not diagnosed prenatally.)

Catanzarite, V, Maida, C, Thomas, W, Mendoza, A, Stanco, L, Piacquadio, KM. "Prenatal sonographic diagnosis of vasa previa". Ultrasound Obstet Gynecol. vol. 18. 2001. pp. 109-15.

(This study evaluated prospective screening for vasa previa using color Doppler ultrasound. 33,208 women were screened, and 11 cases of vasa previa were diagnosed. There was one false positive diagnosis, giving a specificity of 91%. All cases diagnosed survived. There was not, to the knowledge of these authors, any missed diagnosis. This study demonstrated that routine screening for vasa previa is possible.)

Lee, W, Lee, VL, Kirk, JS, Sloan, CT, Smith, RS. "Vasa previa: prenatal diagnosis, natural evolution, and clinical outcome". Obstet Gynecol. vol. 95. 2000. pp. 572-6.

(The authors in this study routinely screened 93,874 pregnant women for vasa previa using gray scale and Doppler ultrasound, and diagnosed 18 cases of vasa previa. This study also demonstrated that screening for vasa previa in a large population is both possible and accurate.)

Robinson, BK, Grobman, WA. "Effectiveness of timing strategies for delivery of individuals with vasa previa". Obstet Gynecol. vol. 117. 2011. pp. 542-9.

(This decision analysis looked at the effectiveness of timing strategies for vasa previa at different gestational ages. The authors found that delivery at 34-35 weeks without amniocentesis was a reasonable balance between the risks of prematurity and that of fetal death.)

Nomiyama, M, Toyota, Y, Kawano, H. "Antenatal diagnosis of velamentous umbilical cord insertion and vasa previa with color Doppler imaging". Ultrasound Obstet Gynecol. vol. 12. 1998. pp. 426-9.

(The authors attempted to determine whether umbilical cord insertion could be reliably and consistently located using ultrasound with color Doppler in 587 pregnancies at 18-20 weeks of gestation. They were successful in 586/587 (99.8%) of cases. The mean time taken was 20 seconds, and 95% of the time, the cord insertion was found in less than 1 minute. This study demonstrates that screening for vasa previa can be done without excessive demands on manpower, equipment or time.)
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