Overview

Vasa previa is a rare but potentially life-threatening condition during pregnancy where fetal blood vessels traverse the membranes covering the cervix, making them vulnerable to rupture. Early diagnosis and timely intervention are crucial to prevent catastrophic outcomes for both the mother and baby. Read on to learn more about Vasa previa, including how it is diagnosed and treated.

What is vasa previa?

Vasa previa occurs when fetal blood vessels run across or near the internal opening of the cervix, unprotected by the placenta or umbilical cord (see diagram below).¹ This abnormal placement of vessels poses a significant risk of rupture during labour or membrane rupture, leading to severe fetal bleeding and potentially fatal consequences.

Although Vasa previa is rare, occurring in approximately 1 in 2500 pregnancies, its impact can be devastating.² Several risk factors increase the likelihood of Vasa previa, including low-lying placenta (placenta previa), multiple pregnancies, in-vitro fertilisation (IVF), and a history of uterine surgeries or caesarean sections.³ Awareness of these risk factors is essential for early detection and management.

Two forms of Vasa Previa - by Sigrid de Rooij; translated into English via Wikimedia Commons.

Types of vasa previa

Vasa previa can be classified into two main types (see diagram above) – Type I and Type II.^1,4

• Type I: Fetal vessels are directly connected to the placental lobes and cross the cervix (left)
• Type II: Fetal vessels connect the umbilical cord to the main part of the placenta, with a portion crossing the cervix (right)

Symptoms and complications

Vasa previa is often asymptomatic, especially in the early stages of pregnancy. However, as the pregnancy progresses, there are a few key signs that might indicate its presence. One of the primary symptoms is painless vaginal bleeding during the second or third trimester.^1,4 This bleeding can be sudden and profuse, signalling the potential rupture of fetal vessels. Since these vessels are not protected by the placenta or the umbilical cord, they are extremely fragile and prone to bleeding.

The complications of Vasa previa are often severe for both mother and baby.¹ For the baby, the primary risk is haemorrhage, which can lead to fetal anaemia, hypoxia (lack of oxygen), and even stillbirth if not promptly managed. The baby’s blood volume is relatively small, so even a minor bleed can have serious consequences. For the mother, the complications are generally related to the emergency interventions required to save the baby. These can include preterm labour, emergency caesarean section, and postpartum haemorrhage, which is a significant cause of maternal morbidity and mortality.

Diagnosis of vasa previa

Recognising the symptoms of Vasa previa and diagnosing it early is vital for the health and safety of both the mother and the baby.^1,4,5 

Prenatal screening methods

Ultrasound imaging 

The primary method for diagnosing vasa previa is through prenatal ultrasound. During routine ultrasounds, usually performed in the second trimester, around 18 to 20 weeks of gestation, the position of the placenta and umbilical cord is carefully examined. High-resolution ultrasound can detect the presence of blood vessels crossing the cervical os, indicative of Vasa previa. The use of transvaginal ultrasound provides an even clearer view, helping to confirm the diagnosis.⁵

Doppler flow studies 

Doppler flow studies complement ultrasound imaging by evaluating the blood flow within the vessels. This non-invasive test uses sound waves to detect the movement of blood within the vessels, highlighting any abnormal flow patterns. Doppler flow studies are instrumental in distinguishing between maternal and fetal blood vessels, ensuring accurate diagnosis of vasa previa.^1,5 

The timing and frequency of diagnostic tests for Vasa previa are critical for ensuring accurate diagnosis and effective management. The initial screening is typically performed during the mid-pregnancy ultrasound, between 18 and 20 weeks of gestation. If Vasa previa is suspected, follow-up ultrasounds and Doppler flow studies are scheduled more frequently to closely monitor the condition. In high-risk pregnancies, additional ultrasounds may be conducted in the third trimester to reassess the position of the vessels and plan for delivery. Continuous monitoring and timely diagnostic tests ensure that both the mother and baby receive the best possible care throughout the pregnancy.

Treatment of vasa previa

Management strategies during pregnancy

Monitoring and surveillance 

Once Vasa previa is diagnosed, close monitoring becomes essential to ensure the safety of both the mother and the baby. Regular ultrasounds and Doppler flow studies are performed to keep track of the position and condition of the blood vessels.² This frequent surveillance helps in the early detection of any changes that could increase the risk of bleeding. Healthcare providers also monitor the baby's growth and development to ensure there are no complications from restricted blood flow.

Hospitalisation and bed rest 

In many cases, women diagnosed with Vasa previa are advised to be hospitalised during the later stages of pregnancy, typically around 30 to 34 weeks. Hospitalisation allows immediate access to medical care in case of an emergency, such as the onset of labour or bleeding.⁶ Bed rest may also be recommended to reduce physical activity and minimise the risk of triggering preterm labour or vessel rupture.

Delivery planning

Timing of delivery

The timing of delivery is crucial in managing Vasa previa. Planned early delivery, usually by caesarean section, is often recommended between 34 to 37 weeks of gestation.² This approach aims to avoid the risk of spontaneous labour, which could lead to the rupture of the fetal vessels. By delivering slightly early, healthcare providers can ensure the baby is born before any complications arise.

Caesarean section vs. vaginal delivery

For women with Vasa previa, caesarean section is the preferred method of delivery. Vaginal delivery is generally avoided due to the high risk of rupturing the exposed blood vessels during labour, which could lead to severe bleeding and jeopardise the baby's life.^2,6 A planned caesarean section provides a controlled environment, reducing the risk of complications and ensuring the safety of both mother and baby.⁷

Emergency interventions

In cases where Vasa previa is diagnosed late or an emergency arises, immediate medical intervention is critical. If bleeding occurs or labour starts unexpectedly, an emergency caesarean section is performed to quickly deliver the baby and prevent severe haemorrhage.⁷ The presence of a well-prepared medical team and readily available surgical facilities in the hospital ensures that any emergencies are managed promptly, minimising risks to both the mother and the baby.

Postnatal care and follow-up

Immediate care for the newborn

Once the baby has been delivered, immediate care is crucial to ensure their health and well-being. Babies born to mothers with Vasa previa may require extra attention, particularly if they were delivered preterm or experienced any complications during delivery. The neonatal team will be ready to provide support, including resuscitation if necessary, and to closely monitor the baby's vital signs. Blood transfusions or other interventions might be necessary if there is significant blood loss during delivery. The baby will be thoroughly assessed for any signs of distress or anaemia and placed in a neonatal intensive care unit if specialised care is required.⁷

Postpartum care for the mother

Postpartum care for mothers who had Vasa previa includes monitoring for any complications such as postpartum haemorrhage, infection, or issues related to the caesarean section.⁷ Pain management and wound care are essential parts of recovery, and the healthcare team will provide guidance on managing these aspects. Emotional support is also crucial, as the anxiety and stress related to a high-risk pregnancy can impact the mother's mental health. Lactation consultants can assist with breastfeeding, especially if the baby is in the neonatal intensive care unit, ensuring the mother can provide nutrition and maintain a connection with her newborn.

Long-term outcomes and follow-up

Both mother and baby will require follow-up appointments to monitor their long-term health and recovery. The baby will need regular paediatric check-ups to assess growth, development, and any potential long-term effects of the early delivery or complications related to Vasa previa. Developmental assessments may be recommended to ensure the baby reaches milestones appropriately.⁷ For the mother, follow-up visits will focus on healing from the caesarean section, managing any ongoing health issues, and providing support for physical and emotional recovery. Early prenatal diagnosis using ultrasound and colour Doppler imaging, hospitalisation or management as outpatients, and caesarean delivery in a tertiary centre with experienced clinicians are the main recommendations for managing Vasa previa.⁸ Continuous monitoring and appropriate interventions can help address any concerns promptly, ensuring both the mother and baby thrive post-delivery.

Summary

Vasa previa is a serious obstetric complication where fetal blood vessels cross or run near the internal opening of the cervix, unprotected by the umbilical cord or placenta, posing a risk of vessel rupture during labour. The primary cause is the abnormal placement of the placenta or umbilical cord. Diagnosis is typically achieved through transvaginal ultrasound with colour Doppler, often during the second trimester. Early diagnosis allows for planned management, including scheduled caesarean delivery before the onset of labour to prevent vessel rupture.

Treatment involves close monitoring and preterm caesarean delivery, around 34-37 weeks of gestation, to ensure maternal and fetal safety. Immediate neonatal care post-delivery is crucial, with potential interventions for any complications from blood loss or prematurity. Postpartum care for the mother includes managing recovery from a caesarean section and monitoring for complications. Emotional support is also vital due to the stress of a high-risk pregnancy. Long-term follow-up ensures the health and development of the baby, addressing any impacts from early delivery. Continuous monitoring of the mother's recovery is essential, promoting both physical and emotional well-being.