Vasa previa is a rare pregnancy condition in which some of the baby’s blood vessels run across or very close to the opening of the cervix, without the protection of the placenta or umbilical cord. It often causes no symptoms during pregnancy, but if these vessels tear, usually when the waters break or labour begins, the baby can lose blood very quickly. When vasa previa is found early by ultrasound and the birth is carefully planned, usually as a scheduled caesarean before labour starts, the outlook for the baby is much better.
What Is Vasa Previa?
During pregnancy, the umbilical cord carries blood between your baby and the placenta. Normally the cord attaches to the centre or body of the placenta, and its blood vessels are protected by a soft, jelly-like tissue called Wharton’s jelly.
In vasa previa, some fetal blood vessels are not protected this way. They travel through the thin membranes of the amniotic sac and pass over, or very near, the internal opening of the cervix. Because they sit in front of the baby’s presenting part, they are at risk of being compressed or torn as the cervix opens, the membranes rupture, or the baby moves down into the birth canal.
The blood in these vessels belongs to the baby, not the mother. A baby has a small total blood volume, so even a small amount of bleeding from these vessels can be serious. This is why vasa previa is considered an important condition to identify before labour.
Causes and Risk Factors
Vasa previa is not caused by anything a mother does or does not do. It results from the way the placenta and umbilical cord develop early in pregnancy. Doctors recognise several situations that make it more likely:
- Velamentous cord insertion: the umbilical cord attaches to the membranes rather than directly to the placenta, so the vessels travel unprotected before reaching the placenta.
- Bilobed or succenturiate placenta: the placenta has two lobes, or an extra smaller lobe, joined by blood vessels that run through the membranes.
- Low-lying placenta or placenta previa in the second trimester: this includes cases where the placenta later moves upward, which can leave vessels behind near the cervix.
- Pregnancy conceived through assisted reproduction, such as IVF.
- Multiple pregnancy, such as twins.
Having one or more of these risk factors does not mean you have vasa previa. It simply means your care team may look more closely during your ultrasound scans.
Symptoms of Vasa Previa
Many women with vasa previa feel completely well and have no warning signs during pregnancy. This is why ultrasound diagnosis is so valuable. When symptoms do appear, they may include:
- Painless vaginal bleeding, especially at the moment the waters break or shortly afterwards.
- Bleeding together with changes in the baby’s heart rate, which may be detected during monitoring in hospital.
- Reduced baby movements, which can be a sign the baby is under stress.
Bleeding in pregnancy has many possible causes, and most are not vasa previa. However, any bleeding in the second half of pregnancy should be checked promptly by a health professional.
How Vasa Previa Is Diagnosed
Vasa previa is usually diagnosed with ultrasound during the second or third trimester. The most reliable method is a transvaginal ultrasound with colour Doppler. A transvaginal scan uses a slim probe placed gently in the vagina to give a clear view of the cervix and nearby structures. Colour Doppler shows blood flow, helping the sonographer see whether vessels are crossing the cervix.
A transvaginal scan is considered safe in pregnancy, including when the placenta is low. Your doctor may suggest it if a routine abdominal scan shows a low-lying placenta, an unusual cord insertion, or an extra placental lobe.
Sometimes a follow-up scan is arranged later in pregnancy, because in a small number of cases the vessels may shift away from the cervix as the uterus grows. Your doctor will explain whether repeat scans are needed in your situation.
What Can Be Done: Managing Vasa Previa Safely
There is no treatment that can move the vessels or make vasa previa disappear. Instead, care focuses on protecting the baby by preventing the vessels from tearing, and on planning the birth before labour starts. A typical plan may include the following.
Close monitoring during pregnancy
You will usually have more frequent check-ups and scans. Your doctor may also check the length of your cervix, since signs of early cervical change can affect timing decisions.
Possible hospital admission in the third trimester
Many guidelines suggest that some women with vasa previa may benefit from staying in hospital, or living very close to one, during the later weeks of pregnancy. This allows immediate access to an emergency caesarean if bleeding or labour begins. Your doctor will discuss whether this is right for you, based on your symptoms, cervical length, distance from the hospital, and personal circumstances.
Medicine to help the baby’s lungs
Because babies with vasa previa are usually delivered a few weeks early, your doctor may recommend corticosteroid injections before the planned birth. These help the baby’s lungs mature and can reduce breathing problems after delivery.
A planned caesarean birth
The safest way to deliver a baby with confirmed vasa previa is generally a planned caesarean section before labour begins and before the waters break. International guidance, such as that from ACOG, commonly suggests planning delivery in the late preterm period, roughly between 34 and 37 weeks. The exact timing is individualised, balancing the risks of early birth against the risk of the vessels tearing if pregnancy continues. A vaginal birth is not recommended when vasa previa is confirmed.
Preparing for the birth
Delivery is ideally arranged in a hospital with a neonatal unit and the ability to provide blood transfusion for newborns if needed. It helps to have a clear emergency plan, know the fastest route to the hospital, and keep your pregnancy records easily accessible.
Self-care tips while you wait
- Follow your doctor’s advice on physical activity and sexual intercourse, as you may be asked to avoid anything placed in the vagina.
- Pay attention to your baby’s movements each day.
- Keep a bag packed for hospital from the second trimester onwards.
- Make sure family members know your diagnosis and what to do in an emergency.
- Look after your emotional wellbeing and share any worries with your care team.
When to See a Doctor
If you have been diagnosed with vasa previa, or if you are unsure, go to the hospital immediately if you notice any of the following:
- Any vaginal bleeding, even if it is light or painless.
- Your waters breaking or a gush or steady leak of fluid from the vagina.
- Regular contractions, tightening, or cramping that may be the start of labour.
- Your baby moving less than usual, or a change in your baby’s normal pattern of movement.
- Pelvic pressure, lower back pain that comes and goes, or a feeling that something is wrong.
Tell the staff right away that you have vasa previa, so they can act quickly. Do not wait to see whether symptoms settle on their own.
Frequently Asked Questions
Is vasa previa dangerous for the mother?
The bleeding in vasa previa comes from the baby’s blood vessels, so the main risk is to the baby. The mother’s health is not usually directly threatened by the condition itself, although she will need a caesarean birth, which carries the usual risks of surgery.
Can vasa previa go away on its own?
In some cases diagnosed in the second trimester, follow-up scans show that the vessels are no longer over the cervix. This is why repeat ultrasound is often recommended. Your birth plan will be based on the findings of your later scans.
Will vasa previa happen again in a future pregnancy?
Vasa previa is linked to the way the placenta and cord develop in each individual pregnancy. Having it once does not mean it will happen again, but your doctor may recommend careful ultrasound checks of the placenta and cord in any future pregnancy.
Will my baby be healthy if born early?
Babies born in the late preterm period often do well, especially when delivery is planned and steroids have been given in advance. Some may need a short stay in a neonatal unit for help with breathing, feeding, or temperature. Your care team will explain what to expect for your baby.
Vasa previa can feel frightening to hear about, but early diagnosis and a clear plan make a real difference. If you have risk factors, notice bleeding, or have questions about your ultrasound results, please speak with your obstetrician and gynaecologist. They can review your situation, arrange the right scans, and work with you on a safe, well-prepared birth plan for you and your baby.
This article is for general education and does not replace examination, diagnosis, or treatment by a doctor. If you have symptoms or concerns, please consult an obstetrician-gynecologist. See our Medical Disclaimer.