Vasa Previa: Symptoms, Types, Causes and Treatment

Vasa previa is a rare but life-threatening obstetric condition that occurs when fetal blood vessels traverse the membranes covering or near the cervical opening, unprotected by the placenta or umbilical cord. If undiagnosed, rupture of these vessels during labor or membrane rupture can lead to rapid fetal blood loss and, in severe cases, fetal death. Thanks to advances in prenatal imaging and increased awareness, outcomes have improved dramatically for babies whose condition is identified before birth. In this article, we’ll explore the symptoms, types, causes, and modern treatment strategies for vasa previa, drawing on the latest research and clinical guidelines.

Symptoms of Vasa Previa

Recognizing the symptoms of vasa previa is crucial, as early detection can be life-saving. However, the condition often remains silent until late pregnancy or labor, making vigilance and targeted screening essential.

Symptom	Description	Clinical Impact	Source(s)
Painless Vaginal Bleeding	Sudden, painless bleeding during labor or after membrane rupture	May indicate vessel rupture and fetal distress	1, 8, 9
Fetal Heart Rate Changes	Rapid fetal heart rate deceleration or bradycardia	Can signal acute fetal blood loss	1, 8, 9
Asymptomatic (Prenatal)	No symptoms before labor or rupture	Most cases detected by screening	8, 9, 12
Signs of Fetal Distress	Decreased fetal movement (rare)	May precede diagnosis in late cases	1, 9

Table 1: Key Symptoms

Overview of Symptoms

Vasa previa is often asymptomatic until a critical event occurs. Most cases are detected through prenatal screening rather than through symptoms alone, which is why routine imaging in at-risk pregnancies is so important 8, 9, 12.

Painless Vaginal Bleeding

The hallmark symptom of undiagnosed vasa previa is sudden, painless vaginal bleeding during labor or immediately following rupture of the membranes (the “water breaking”). This bleeding originates from fetal—not maternal—vessels, and even a small amount can be catastrophic for the baby due to their limited blood volume 1, 8, 9.

Fetal Heart Rate Changes

Acute fetal blood loss leads to rapid changes in the fetal heart rate, typically a sudden deceleration or persistent bradycardia detected on fetal monitoring. These changes may be the first sign that something is wrong if vasa previa was not previously identified 1, 8.

Asymptomatic Cases (Prenatal Detection)

Most vasa previa cases identified before labor are asymptomatic. The diagnosis is made during a routine second-trimester ultrasound, often as part of screening for other placental or cord abnormalities 8, 9, 12.

Signs of Fetal Distress

In rare cases, parents may notice decreased fetal movement, which can indicate fetal distress after significant blood loss. However, this is not a reliable or early symptom and underscores the need for routine screening in high-risk pregnancies 1, 9.

Types of Vasa Previa

Vasa previa is not a uniform condition. It is classified into different types based on the anatomical relationship between the fetal vessels, placenta, and umbilical cord. Understanding these types is critical for accurate diagnosis and management.

Type	Description	Key Features	Source(s)
Type I	Fetal vessels connect a velamentous umbilical cord to the placenta, crossing the cervix	Most common; linked with velamentous insertion	1, 2, 3
Type II	Vessels connect the main placenta to a succenturiate (accessory) lobe or between lobes, crossing the cervix	Associated with bilobed or succenturiate placentas	1, 2, 3
Type III	Aberrant vessels near the internal os without classic risk factors; normal placental shape and cord insertion	Fewer risk factors; harder to diagnose	2, 4, 5

Table 2: Vasa Previa Types

Type I: Velamentous Cord Insertion

Type I is the most recognized form, where the umbilical cord inserts into the membranes (not directly into the placental disk), and fetal vessels run unprotected across the membranes, often directly over the cervix. This type is closely associated with velamentous cord insertion 1, 2, 3.

• Key features: More than one aberrant vessel may be present. Risk factors include IVF and velamentous cord insertion 2.

Type II: Succenturiate or Accessory Lobe

In Type II, fetal vessels connect a main placenta to an accessory (succenturiate) or bilobed placenta. These connecting vessels may traverse the lower uterine segment and internal cervical os, making them vulnerable 1, 2, 3.

• Key features: Frequently linked to bilobed or succenturiate placentas. May be associated with a higher placental and fetal birth weight compared to Type I 3.

Type III: Atypical or Isolated Fetal Vessels

Recently described, Type III vasa previa includes cases not fitting the first two types. Here, vessels are near the internal os despite normal cord insertion and placental morphology. These are harder to diagnose, as typical risk factors are absent and only a single aberrant vessel may be seen 2, 4, 5.

• Key features: May present without classic imaging findings. Requires high suspicion and careful Doppler evaluation 2, 4.

Causes of Vasa Previa

Understanding what causes vasa previa is key to identifying at-risk pregnancies and guiding screening strategies. The condition arises from abnormal placental or cord development, and several risk factors are now recognized.

Cause/Risk Factor	Mechanism or Association	Frequency in Vasa Previa	Source(s)
Velamentous Cord Insertion	Cord inserts into membranes instead of placenta	52% of cases	1, 6, 8
Succenturiate/Bilobed Placenta	Additional or bilobed placental tissue with connecting vessels	33% of cases	1, 6, 8
Low-Lying Placenta/Placenta Previa	Placenta near internal cervical os in second trimester	61% of cases	6, 8
In Vitro Fertilization (IVF)	Assisted reproduction increases placental abnormalities	26% of cases	1, 6, 8
Multiple Gestation	Twin or higher-order pregnancies	~9% of cases	6, 8
No Obvious Risk Factors	Seen in some Type III cases	Uncommon but possible	2, 5

Table 3: Causes and Risk Factors

Velamentous Cord Insertion

This is the most significant single risk factor for vasa previa. Here, the umbilical cord inserts into the fetal membranes rather than the placental disk, leaving vessels vulnerable as they travel unprotected to the placenta 1, 6, 8.

• Detected in over half of vasa previa cases 6.
• Strongly associated with both spontaneous and assisted conceptions.

Succenturiate or Bilobed Placenta

A succenturiate (accessory) lobe or a bilobed placenta can have connecting vessels crossing the lower uterine segment. These vessels are prone to being stretched or ruptured during labor or membrane rupture 1, 6, 8.

• Present in about one-third of vasa previa cases 6.
• Increases the risk of both Type II and Type III presentations 2, 4.

Low-Lying Placenta or Placenta Previa

Placenta previa or a low-lying placenta in the second trimester can predispose to vasa previa, especially if the placenta migrates upward but leaves exposed vessels near the cervical os 6, 8.

• Affects over 60% of vasa previa pregnancies 6.

In Vitro Fertilization (IVF)

Pregnancies conceived via IVF are at higher risk, possibly due to abnormal implantation and placental development. This may explain the increased frequency of velamentous cord insertion and accessory lobes in these pregnancies 1, 6, 8.

• IVF accounts for about a quarter of vasa previa cases 6.

Multiple Gestation

Twin or higher-order pregnancies have an elevated risk, likely due to increased placental complexity and abnormal cord insertions 6.

Absence of Risk Factors: Type III Vasa Previa

Some cases, particularly Type III, occur without any of the classic risk factors or abnormal placental findings. These can only be detected by careful imaging and highlight the importance of routine placental evaluation during the second-trimester scan 2, 5.

Treatment of Vasa Previa

Effective treatment of vasa previa focuses on preventing vessel rupture by ensuring timely delivery before labor or membrane rupture occurs. Advances in screening and new therapies are transforming outcomes for affected pregnancies.

Approach	Key Elements	Outcome/Goal	Source(s)
Prenatal Diagnosis	Ultrasound with color Doppler at 18-26 weeks	97-99% survival	1, 8, 9, 11
Hospitalization & Surveillance	Inpatient care from 30-34 weeks for some patients	Close monitoring, timely intervention	1, 11, 12
Planned Cesarean Delivery	Delivery at 34-37 weeks before labor or rupture	Prevent vessel rupture, optimize neonatal outcome	1, 8, 9, 10, 12
Antenatal Corticosteroids	Given at 28-32 weeks if early delivery likely	Fetal lung maturity	11, 12
Fetoscopic Laser Ablation	Minimally invasive ablation of vessels (Types II/III)	May allow term vaginal birth	4
Neonatal Support	Immediate transfusion and resuscitation if bleeding occurs	Reduce mortality/morbidity	1, 7, 9

Table 4: Treatment Strategies

Prenatal Diagnosis: The Cornerstone

The most critical advance in vasa previa care is prenatal diagnosis using targeted ultrasound and color Doppler imaging, typically performed during the second-trimester anatomy scan (18-26 weeks). Detection rates are now over 90%, drastically improving survival rates, which now exceed 97% when the diagnosis is made before labor 1, 8, 9, 11.

• All at-risk pregnancies should have placental cord insertion and lower uterine segment evaluated with color Doppler 12.

Hospitalization and Surveillance

In some cases, especially when risk factors for preterm labor are present, patients may be hospitalized starting between 30-34 weeks for close monitoring. This allows for rapid intervention if labor starts or bleeding occurs 1, 11, 12.

• Outpatient management may be reasonable for asymptomatic, low-risk cases 12.

Planned Cesarean Delivery

A scheduled cesarean section is recommended before labor begins, usually between 34 and 37 weeks, to prevent spontaneous rupture of membranes and catastrophic fetal bleeding 1, 8, 9, 10, 12. The precise timing is individualized, balancing the risks of prematurity against the dangers of vessel rupture.

• Cord clamping is performed promptly to prevent further fetal blood loss if a vessel is encountered during delivery 1.

Antenatal Corticosteroids

If early delivery is anticipated, corticosteroids are administered between 28-32 weeks to promote fetal lung maturity and reduce the risks of complications from prematurity 11, 12.

Fetoscopic Laser Ablation

For select cases of Types II and III vasa previa, fetoscopic laser ablation—a minimally invasive procedure to seal off vulnerable vessels—can be considered. This approach, performed in specialized centers, may allow for term vaginal delivery and avoids prolonged hospitalization, with favorable outcomes reported 4.

• Not recommended for Type I vasa previa 4.

Neonatal Support

Despite best efforts, some cases present unexpectedly during labor or after rupture of membranes. Immediate neonatal support with transfusion, resuscitation, and intensive care is vital to improve outcomes if significant fetal bleeding has occurred 1, 7, 9.

Conclusion

Vasa previa, while rare, represents a critical obstetric emergency if not recognized before labor. Advances in ultrasound screening, understanding of risk factors, and new treatment approaches have dramatically improved outcomes for affected babies and families. Early recognition and evidence-based management are key.

Main points:

• Vasa previa is often asymptomatic until membrane rupture, at which point painless vaginal bleeding and fetal distress occur.
• There are three main types: Type I (velamentous cord), Type II (accessory or bilobed placenta), and Type III (atypical, harder to diagnose).
• Major causes include velamentous cord insertion, succenturiate or bilobed placentas, low-lying placenta, IVF, and multiples; some cases have no risk factors.
• Prenatal diagnosis using ultrasound and color Doppler is essential and has transformed outcomes.
• Management includes planned preterm cesarean, possible hospitalization, corticosteroids, and, in select cases, fetoscopic ablation.
• Prompt neonatal support is crucial if rupture and bleeding occur.

With vigilant screening and multidisciplinary care, vasa previa can be managed safely, offering hope and reassurance to families facing this high-risk diagnosis.