Frequently Asked Questions

1. Pathology of Vasa Previa

1.1. How does vasa previa occur?

The theory about this that makes most sense is called Trophotropism. The easiest way to explain this is to make a comparison to a plant. A plant will lean towards the sun to get the light it needs to survive. Since the lower segment of the uterus is not as nourishing as the upper segment, the placenta will grow to reach more nourishing tissue. The placental mass will erode away from the cervix, but the vessels can't. This also explains the velamentous insertion of the cord. That the mass may erode and the new growth may occur away from the location where the cord inserts.

1.2. How similar are cord prolapse and vasa previa? With a cord prolapse there are also blood vessels (although protected by Wharton's jelly) in front of the cervix. Does vasa previa require unprotectedvessels?

Vasa previa vessels are adherent to the membranes over the cervix, and they can be torn open with cervical dilation. Cord prolapse is of a free floating umbilical cord which happens to be presenting in front of a cervix which dilates, allowing the cord to enter the canal and then becomes compressed as the head of the baby enters the canal.

1.3. How dangerous is velamentous cord insertion with a high placenta?

Velamentous cord insertion is relatively common with an estimated incidence of 1:100 singleton pregnancies. When located in the upper segment of the uterus the risks are not as great as when located in the lower segment, although there is a chance that they could tear during the third stage of labour when the placenta is being delivered if the cord is pulled. Velamentous cord or succenturiate lobed with connecting vessels away from the cervix is of little clinical importance most of the time. A velamentous cord may have a more delicate origin and be at risk of torsion and obstruction. There may or may not be consequences for fetal growth and for twin transfusion syndrome -- some not well validated observations suggested in some medical articles.

1.4. Is velamentous cord insertion dangerous by itself, without having vasa previa?

Yes, velamentous cord insertion can be dangerous when the unprotected blood vessels are not crossing the cervix, but are located in the lower segment of the uterus. Depending on the extent of the exposed vessels and where they are located they may be at risk of rupture or compression late in pregnancy.

1.5. How common is velamentous cord insertion?

Published sources suggest that velamentous cord insertion occurs about 1-2 times per 100 pregnancies. Figures vary depending on whose study you read. Vasa previa is generally said to occur about 1:2-3000 pregnancies.

1.6. What are the causes of velamentous cord insertion?

Placental remodeling.

1.7. Could you say that there is only risk of velamentous cord insertion when the cord inserts marginally? What causes a cord to insert marginally? Is this something that could be inherited?

Velamentous cord is one step beyond a marginal insertion -- an exaggeration of the same process. The term "trophotropism" has been used to explain that a placenta seeks a best blood supply and can grow in the direct of favorable blood supply and can atrophy where the blood supply is less favorable. Lower uterine blood supply is less optimal than higher up. If the placenta implants low, it may "migrate" by differential proliferation and atrophy. Each existing part of the placenta remains where it formed, however, including the cord insertion. If about half the placenta "melts away", a marginal cord occurs. If the migration is more extreme, velamentous cord insertion occurs, and if the placenta was initially a previa, vasa previa may be the result.

1.8. Has vasa previa or velamentous cord insertion been related to a higher incidence of birth defects than those born without vp or vci?

No, most of these babies are totally normal. VCI and vasa previa are associated with a higher incidence of poor outcome.

1.9. The chances of vasa previa recurring are said to be 1:3000, the same chance as for any other woman. A low-lying placenta, or placenta previa, are likely to re-appear though, because of damage in the other regions of the uterus. Is velamentous cord insertion likely to re-appear?

There is no objective evidence of an increased likelihood of vasa previa after a first case, but your proposed risk factor comments have some potential chance of affecting future placentation. But the likelihood of a repeat  is very, very low.

1.10. The placenta is developed from the baby, then implanted to the mother. Since the baby is made of both mother and father could there be a genetic factor involved for having velamentous cord insertion? If so, would that be from the mother's genes or from the baby's genes?

The concept of how the cord and the placenta form is somewhat different from what you wrote in this question. The egg is fertilized by the sperm while it is still in the tube (salpinx), and it starts to divide into a multi-celled ball called the blastocyst. This will later differentiate into the fetus, cord, and the fetal tissue of the placenta called the Trophoblastic villi. The blastocyst enters the uterus from the tube, probably wanders around for a day or more, and eventually implants in the wall of the uterus. The site of implantation is thought to be selective, trying to achieve a site with good blood supply, more often high than low in the uterus, as was mentioned before. Certain conditions may predispose to a low implantation, especially uterine scars as from cesarian section deliveries in prior pregnancies. Wherever the blastocyst implants will be the initial site of the placenta. It is thought that the placenta starts as rounded disk with the cord insertion at its center. The fetal tissue differentiates from the placenta at the blastocyst stage, with the fetus separating and linked by the developing cord. Low implantations of placenta have a strong tendancy to migrate upwards toward the body and fundus of the uterus, which can shift the cord (which remains where it initally formed relative to the underlying uterine wall) toward a marginal or even velamentous insertion. In effect the placenta atrophies out from under the cord, which remains where it was at implantation. There is no evidence of genetic predisposions within families to account for velementous cords. It is believed that the occurence is specific to the vascular supply and peculiarities of an individual uterus, including any scarring whether from operations, infections, or prior pregancy complications.

1.11. The chances of velamentous cord insertion are 1:50. Does the combination low-lying placenta (or placenta previa) and velamentous cord insertion automatically result in vasa previa? In other words: does a velamentous cord insertion always occur at the bottom of the placenta or could it also be at the top? If it is always at the bottom, is it safe to say that women with a low-lying placenta have a 1:50 chance of vasa previa?

The risk of occurrence of velamentous cord insertion is variably reported, in one reference book it was listed at between 1:1000 and 1:55, (the textbook obviously quoting a variety of different published medical articles). Experience would suggest a less frequent occurrence than 1:50 you gave. The presence of an initial previa, with trophotropism then producing remodeling, is the mechanism that is thought to lead to velamentous cords. Whether there will or will not be vasa previa depends on the initial location of the cord insertion and the direction toward which the placenta migrates/atrophies. There is no obligate situation which must produce a vasa previa.

1.12. Is a low lying placenta only dangerous because it increases the risks on vasa previa when you are having velamentous insertion? Or does a low-lying placenta also increase the chances of velamentous insertion?

It would be most likely with a velamentous cord insertion in a low-lying placenta only because of proximity to the cervix. A velamentous insertion on a placenta higher in the uterus is not a significant consequence most times.

1.13. Can vasa previa improve as the pregnancy progresses?

Occasionally. Unlike a placenta previa the vessels involved in a vasa previa are unlikely to erode away (which is how a placenta previa seemingly "moves"). There is a chance that this vessel will become thrombosed (plugged). This would take away the risk of fetal bleeding, but whether the baby would tolerate this depends on what proportion of the blood flows through this vessel. With increasing rates of early diagnosis of vasa previa during the 18-20 week morphology ultrasound we are hearing of more cases where the vasa previa does not persist until term. Although the vessels do not go away or move on their own, when the lower segment of the uterus forms in the later part of pregnancy, the expansion can lead to an increase in distance between the vessels and the cervix. This is not a true “resolution” of vasa previa but in some rare cases it may allow for a vaginal delivery. There is currently no evidence about what is considered to be a “safe” distance between the exposed vessels and the cervix, However keeping in mind that the cervix dilates to 10cm across for birth, any vessels within that area may be at risk. While 2cm may be considered safe for placenta previa we do not believe that is the case for vasa previa.

1.14. Could vasa previa cause a placental abruption?

They are not related at all.

1.15. Is the prognosis for the bi-lobed/succenturiate lobed vasa previa better than that of the velamentous insertion of the cord vasa  previa? Is there less risk for growth abnormalities?

Presumably both situations, bi-lobed/succenturiate lobed and velamentous insertion, are at risk and should be managed similarly.

1.16. Can bi-lobed placenta lobes grow together and become one huge massive placenta?

The placenta can change during pregnancy but little is documented as to how.

1.17. How often do bi-lobed placentas recur?

The answer to this is not known.

1.18. What would be the percentages of vasa previa happening again after having a bi-lobed placenta?

The answer to this is unknown.

1.19. What is the likelihood of having a repeat low-lying placenta?

There are no studies looking at this issue.

1.20. What is the likeliness of a reoccurrence of vasa previa or velamentous insertion in a subsequent pregnancy?

This is unknown. No one has data on recurrence risk for vasa previa; nevertheless it is extremely low....You cannot reduce your risk of a recurrence. Don't worry, the risk is low. See a perinatologist to do a thorough sonogram. There are several other complications of pregnancy that can be dangerous. The risks of any of these are much higher than the risk of recurrent vasa previa. See a good OB/GYN and one that you trust and have good rapport with.

1.21. Are there any cases known in which a woman has had vasa previa and/or velamentous cord insertion in more than one pregnancy?

The IVPF has learned of several women who had vasa previa during their subsequent pregnancies, including one who had it three times in total; however this information has not been documentedin the published literature.

1.22. Why do so many vasa previa babies seem to be breeched or traverse?

Most likely the transverse lie is related to the low-lying placenta. When the placenta occupies the lower portion of the uterus, it prevents the head from engaging (going into the lower segment of the uterus, and the pelvis). Therefore, the baby may not be head first. The position of the vasa previa baby may also reflect an attempt by the baby to avoid compression of the velamentous vessels.

1.23. What are common factors in each of the women who have had vasa previa?

Vasa previa does have an association with a low-lying placenta, which may be associated with previous uterine surgery including prior cesarean, maternal smoking, multiple pregnancy (twins, triplets, etc), and also with assisted conception (artificial insemination, in-vitro fertilization, etc).

1.24. What can one do to reduce the chances of a second occurrence of vasa previa in a subsequent pregnancy?

The answer to this is unknown. Again, recurrence risk is low...

1.25. What lifestyle factors or medical conditions increase the likelihood of vasa previa?

The answer to this is unknown. There are no lifestyle changes that affect the incidence of vasa previa. However, vasa previa does have an association with a low-lying placenta, which may be associated with prior cesarean, maternal smoking, multiple pregnancy, and also with assisted conception.

1.26. How many babies still die due to vasa previa even with a diagnosis during the pregnancy?

Published data from retrospective case studies on vasa previa shows a variable mortality rate of 30-100%. Data suggests that survival is practically 100% if the diagnosis of vasa previa is made prenatally, and the baby is delivered by elective cesarean section prior to the onset of labor. Unfortunately we still see deaths from vasa previa either due to a lack of prenatal diagnosis or inappropriate management following diagnosis.

2. Diagnosing Vasa Previa

2.1. Why is it that so many OB/GYN’s don't seem to have up-to-date information on vasa previa? And why do most of them seem to take a very "can't do anything about it anyway" attitude towards vasa previa?

Vasa previa can be diagnosed prenatally. The time has come when physicians should look actively for it. The tragedy of fetal death from a ruptured vasa previa is preventable in the majority of cases. There is little educational opportunity for the obstetrical provider to study umbilical cord accidents.

2.2. What kind of success does the new 3D ultrasound have with diagnosing vasa previa? How does it compare to the color Doppler ultrasound?

The constant improvement in ultrasound will allow more accurate diagnosis of vasa previa.

2.3. After having vasa previa once, should one be insistent with their doctor to have a color Doppler ultra sound with any future pregnancies?

There is no evidence of vasa previa repeating in subsequent pregnancy. An ultrasound review of the placenta and cord would be important anyway.

2.4. If a doctor knew that one had a low-lying placenta AND a bilobed placenta, should he have also known that the patient was a very good candidate for vasa previa?

Unfortunately physicians are often poorly educated about vasa previa; furthermore they often consider the condition to be rare. Therefore, they are often caught totally unaware when vasa previa does occur. The key is in a high index of suspicion.  So the message we are trying to get out is that all physicians should be suspicious and look for vasa previa. Even the best sonographer will miss vasa previa if not on the lookout for it. There definitely needs to be more education about ultrasound of the placenta and umbilical cord.

2.5. Is there any way to detect velamentous cord insertion before birth?

Yes. Velamentous insertion can be detected prior to birth using ultrasound, certainly with color Doppler ultrasound.

3. Management of Vasa Previa

3.1. If a patient is diagnosed with vasa previa, what should she be doing to help her situation? What are her chances of normal delivery with this condition?

The main issue will be awareness of the problem, close follow of the pregnancy and likely limiting activity and sexual activity following 24 weeks of the pregnancy-much as you would with a placenta previa. Delivery will have to be via cesarean section and probably electively in advance of your due date to avoid rupture of membranes and/or labor with cervical dilation. Vaginal examination should be avoided.

3.2. Fetal death associated with vasa previa is said to be as high as 75 percent. Are the odds any better if diagnosis was made antepartum?

Most of the deaths described occur acutely after the bag of waters breaks and tears the vessel. Recognition of the problem can be delayed because of the normal "bloody show" that occurs as the cervix dilates. If this occurs at home then the likelihood of delivering baby in time to prevent death or injury becomes very unlikely. The other situation where problems for the baby occur is when the presenting part, usually the baby's head drops so low into the pelvis that the vessel gets compressed, stopping blood flow. Again, whether this is a problem depends on how much blood is flowing through the vessel supplying the baby with oxygen. Knowing that the vessel is in a vulnerable position from both types of injury improves the likelihood of a good outcome. The biggest problem is trying to predict if and when such an event might occur. Hence the suggestion that you will spend some time in the hospital before baby is born.

3.3. How likely is third trimester bleeding with vasa previa?

With a vasa previa not associated with abnormal placental implantation (some form of placental previa) there should be no increase in third trimester bleeding. Bleeding from a vasa previa only occurs if the vessel is torn or ruptures.

3.4. Placenta previa bleeding can be stopped and the pregnancy can progress. Is this possible with vasa previa?

No. There is nothing that we actively do to stop bleeding from a placenta previa. Bleeding from a placenta previa occurs because the attachment of the placenta to the uterus breaks (peels off). Often the bleeding stops as a result of the formation of blot clots in the area that has separated. Bleeding from a vasa previa occurs because the vessel has been torn. Possibly the vessel could spasm and close down flow, but flow is usually so brisk that clots get washed away before they can seal the tear.

3.5. How is this condition managed? At what point, if any, are patients admitted to the hospital? If there is bleeding, how much time can pass before the baby is at risk? Can an emergency C-section be performed that quickly?

The condition is usually managed by a cesarean delivery. The timing of the cesarean is where there is some controversy. One would like it to be late enough in the pregnancy that the baby is mature and has no problems of prematurity. However, the later one waits then the more likely that an emergent situation arises. There is no good answer as to how long a baby can hold out before beginning to have problems. An emergency cesarean can be performed quickly if someone is in the hospital. Whether or not it can be done "quick enough" is uncertain and unfortunately even in the best of circumstances baby can be at risk. The International Vasa Previa Foundation recommends hospitalization in the third trimester and delivery by C-section at approximately 35-36 weeks. All management plans should be based on individual consultation with suitably qualified obstetrician.

3.6. Once vasa previa is diagnosed prenatally, what should the course of action be...

        ...complete bed rest or just activity restrictions?

Bed rest is not essential. However, a reduction in activity is desirable as is avoidance of sexual intercourse, and the mother should be admitted in the third trimester as previously discussed.

        ...when should you be admitted to the hospital?

When vasa previa is diagnosed prenatally, it makes sense to hospitalize the mother in the third trimester (possibly around 31-32 weeks), and deliver the baby by cesarean section at about 35-36 weeks. She may require delivery earlier should bleeding occur. Why hospitalize the mother? In the event that the membranes should rupture and bleeding ensues, rapid delivery is possible in hospital, whereas in the time it takes the mother to arrive in hospital from home, the fetus will most likely be dead. Doctors regularly admit women with preterm labor, pre eclampsia, placenta previa and other conditions which are not associated with perinatal mortality anywhere near as high as vasa previa.

        ...should you be monitored constantly while there?

Monitoring in hospital does not necessarily need to be excessive. A fetal heart tracing each day should be adequate (this is done in most hospitals for all obstetric in patients). The reason for admission is to be able to act in the event of rupture of the membranes and bleeding, not primarily for monitoring.

        ...what course of action should be taken for preterm contractions?

Preterm contractions should be treated with drugs to stop them (tocolytics). Persistent preterm contractions leading to labor are an indication to consider Cesarean delivery, especially if the fetus is mature and steroids have been given. what point should the baby be delivered early even if the lungs may not be mature rather than risk rupturing?

Thirty-six weeks appears a reasonable gestational age to schedule delivery. Most fetuses will have mature lungs at this gestational age. Certainly, death of lung immaturity at 36 weeks is virtually unheard of, provided the mother is not diabetic and the dates are accurate. Compare this with the risk of death or poor outcome should the membranes rupture. Education of the patient and expectant delivery at the least evidence of labor is essential!

3.7. Is there any risk having a bi-lobed placenta if the connecting vessels aren't crossing the cervix?

A bilobed placenta carries some risk even when the connecting vessels do not overlie the cervix.  The connecting vessels may rupture. Velamentous insertion, even when not vasa previa (not overlying the cervix) is more frequently associated with fetal abnormalities and poor obstetric outcome. The risk is lower than with vasa previa, but still these patients may require more intensive monitoring.

3.8. After having had vasa previa once, should one be insistent with their doctor to have a color Doppler ultra sound with any future pregnancies?

There is no evidence of vasa previa repeating in subsequent pregnancy. An ultrasound review of the placenta and cord would be important anyway.

3.9. If a woman has velamentous cord insertion, but not vasa previa, is it safe to deliver vaginally?

Though it is common to deliver with a VCI without detriment to the baby, VCI carries risk even when not a vasa previa. VCI may be allowed a trial of labor if the vessels are away from the cervix. However, close continuous monitoring is mandatory. The vessels could rupture, and also pressure on the vessels could lead to fetal compromise. This can be detected early by monitoring.