Vasa Praevia: When to Look Closer

by Ben Sweetlove | Sep 15, 2026 | Pregnancy, QUFW News

Vasa praevia is a near-perfect example of a condition where ultrasound can genuinely change a pregnancy’s outcome. Vasa praevia can be silent; the baby gives no warning, and the only thing standing between a safe, planned birth and a preventable tragedy is early diagnosis in experienced hands.

Patients diagnosed with vasa praevia have emphasised the importance of receiving clear, evidence-based information about the risks and benefits of different care pathways. The primary benefit of screening for vasa praevia is that antenatal diagnosis significantly increases the likelihood of perinatal survival.

This post summarises current best practice, drawing on the RANZCOG guideline Vasa Praevia (C-Obs 47), Version 3 (July 2025), the most relevant evidence-based resource for practice in Australia and Aotearoa New Zealand. Written for referring GPs and clinicians, it covers what vasa praevia is, why it matters so much at delivery, the histories and findings that should raise your index of suspicion, and when targeted specialist assessment is worth arranging. (You may also see it written as vasa previa, the spelling used in much of the international literature; the two terms describe the same condition.)

Table of contents

1. What is vasa praevia?
2. Why diagnosis matters
3. Who is at risk?
4. How is vasa praevia diagnosed?
5. When to refer to a tertiary unit
6. Delivery and management
7. Refer your patient to QUFW

What is vasa praevia?

Vasa praevia is the presence of unprotected fetal blood vessels within the amniotic membranes over or near the cervical os. Rupture of the membranes before or during labour may result in fetal death from rapid blood loss if an unprotected fetal blood vessel near the cervix is damaged.

Three types are described:

• Type 1 – characterised by a velamentous insertion of the umbilical cord onto the membranes distant to the placenta, with the vessels traversing the membranes over the cervix before reaching the placenta.
• Type 2 – characterised by a succenturiate, multilobed or bilobed placenta with fetal vessels connecting the lobes overlaying the cervix.
• Type 3 – characterised by abnormal fetal blood vessels branching off the placenta and lying unprotected near the cervical os, arising after resolution of placenta praevia or low-lying placenta.

A systematic review of 24 observational studies reported 1 case of vasa praevia for every 1,271 pregnancies (95% CI 990 to 1,692) (Zhang et al., 2023). Australian data suggest a lower rate as cited in Sullivan et al. (2017) with 63 cases from approximately 294,045 pregnancies, or 1 in 4,673. The lower Australian incidence may be explained in part by low multiple pregnancy rates arising from single embryo transfer policies (RANZCOG, 2025).

Why diagnosis matters

Screening programs for vasa praevia have been shown to be highly sensitive. When vasa praevia is not diagnosed before labour, the estimated perinatal mortality is ==44% to 70% (RANZCOG, 2025)==, and that mortality persists even with an urgent caesarean once a vessel has ruptured. The classic intrapartum presentation is painless dark-red vaginal bleeding after rupture of membranes, accompanied by acute fetal compromise. By the time this happens, the window to act is narrow.

When the diagnosis is made antenatally and a planned caesarean is performed before labour, perinatal survival is 98.6% (95% CI 96.7 to 99.7%), compared with 72.1% (95% CI 50.6 to 89.4%) where no antenatal diagnosis is made (Zhang et al., 2021). Intact perinatal survival, meaning survival without severe impairment, shows the same pattern: 96.7% with an antenatal diagnosis against 28.1% without (Zhang et al., 2021).

In short, the condition is almost entirely survivable if found in time, and frequently fatal if not. That dichotomy is what justifies screening and vigilance.

Who is at risk?

Approximately 83% of women with vasa praevia have at least one identifiable risk factor (RANZCOG, 2025). The strongest ultrasound predictors are a low-lying placenta and a velamentous cord insertion.

Pooled prevalence of each risk factor among vasa praevia cases (Pavalagantharajah et al., 2020):

Risk factors are common, and most women with them will not have vasa praevia. Velamentous cord insertion occurs in roughly 2% of pregnancies, while vasa praevia affects approximately 0.08%. Risk factors raise the index of suspicion and determine who needs a follow-up scan but they are not the diagnosis itself.

It is also worth noting that findings identified in the second trimester frequently resolve. Vasa praevia resolves in 14% to 39% of cases, with resolution far more likely when the finding is made before 24 to 26 weeks (RANZCOG, 2025). This is precisely why the diagnosis is confirmed later in pregnancy rather than applied at the morphology scan.

How is vasa praevia diagnosed?

Diagnosis is made with ultrasound, and RANZCOG describes a two-stage pathway.

Screening — 20 to 22 week morphology scan. RANZCOG suggests all women be offered screening for vasa praevia at the time of the second trimester anatomy scan (Evidence-based recommendation 1). A good quality report will comment on the location of the placental cord insertion, the morphology of the placenta, and clear documentation of a colour Doppler sweep of the cervix to assess for low-lying fetal vessels. At this stage, no distinction is drawn between vasa praevia and low-lying fetal vessels: any fetal vessels within 50 mm of the internal cervical os are characterised as low-lying fetal vessels.

Diagnosis — transvaginal ultrasound at 28 to 32 weeks. Where any of the following are present at the morphology scan, or where a woman with risk factors has not had a previous scan, the diagnosis should be confirmed by transvaginal ultrasound at 28 to 32 weeks, or earlier if clinically indicated (Evidence-based recommendation 2):

• low-lying fetal vessels (within 50 mm of the cervical os)
• velamentous cord insertion
• low-lying placenta
• bilobed or multilobed placenta

At that third trimester scan, fetal vessels within 20 mm of the cervical os identified by transvaginal ultrasound are diagnostic of vasa praevia (Evidence-based recommendation 3). Vessels between 20 mm and 50 mm are defined as low-lying fetal vessels, and vessels beyond 50 mm require no further investigation for vasa praevia.

Transvaginal ultrasound with Doppler is the preferred approach for evaluating the cervical os and lower uterine segment, providing high resolution of small vessels and a more accurate assessment of the vessel-to-os distance. Where vessels remain within 50 mm at the early third trimester scan, a repeat scan at or after 32 weeks should be considered to confirm their final location.

3D Rendered Volume with Colour Doppler

There is no international consensus on the distance that defines vasa praevia. In a 2024 survey of 57 experts, 34% used a 20 mm threshold, 32% used 50 mm, and 21% did not rely on distance at all (RANZCOG, 2025). The RANZCOG thresholds represent a pragmatic position rather than a settled one.

When to refer to a tertiary unit

For GPs and clinicians in shared-care or community settings, the referral triggers are straightforward:

• A suspected or confirmed finding on ultrasound should prompt referral to specialist obstetric care for a confirmatory transvaginal scan at 28 to 32 weeks, and ongoing management planning.
• Suspected vasa praevia, together with clinical features of preterm labour or antepartum haemorrhage occurring before the third-trimester confirmatory scan, warrants consultation with a Maternal Fetal Medicine (MFM) specialist for management of the pregnancy.
• At the extremes of prematurity, or where the diagnosis is uncertain, MFM consultation is again advisable to balance the competing risks.

An equivocal or incomplete view of the cord insertion or the vessels near the os is reasonable grounds to refer for a closer look. The aim is simply to ensure that, where the risk exists, the vessels have been specifically assessed. When vasa praevia is excluded, that is genuine reassurance for the patient and for you. When it is identified, a clear plan can be implemented.

Delivery and management

Once vasa praevia is confirmed, patient management centres on planning a caesarean birth before the onset of labour, while weighing the risks of prematurity against the risk of vessel rupture. Care should be individualised and discussed in the context of patient preferences and individual circumstances.

For asymptomatic women with confirmed vasa praevia, inpatient versus outpatient management from 32+0 weeks should be discussed rather than mandated. Outpatient management is reasonable for asymptomatic women, particularly those without additional risk factors and with good access to emergency services. When weighing this up, consider additional risk factors for preterm labour multiple gestation, a short cervix, or a history of preterm birth. Women with low-lying fetal vessels (20 to 50 mm) can generally be managed as outpatients with ongoing antenatal care and birth planning.

Current guidance on timing of birth, balancing prematurity against the risk of vessel rupture in labour (RANZCOG, 2025):

• Asymptomatic, no preterm-birth risk factors: consider caesarean from 36+0 weeks. Evidence suggests 36+0 to 36+6 weeks may best balance the risks of prematurity against those of vasa praevia complications.
• Risk factors for preterm birth present: consider caesarean from 34+0 weeks.
• Symptomatic (bleeding, preterm labour): consider urgent caesarean, balancing the risks of prematurity against the likelihood of fetal compromise.

Birth planning should be guided by clinical features, patient preferences, and access to specialist obstetric and neonatal services, with the aim of ensuring birth before the onset of labour or complications.

Refer your patient to QUFW

At QUFW, our consultants are subspecialist obstetricians and gynaecologists with extensive experience in high-risk pregnancies. Vasa praevia is uncommon, but primary care providers should offer a routine ultrasound at 20 to 22 weeks (morphology scan) to assess for this condition in all pregnancies.

If you would like to contact us to discuss a patient you would like assessed, or if your patient would like to book an appointment, click here.

References

Pavalagantharajah, S., Villani, L. A., & D’Souza, R. (2020). Vasa previa and associated risk factors: A systematic review and meta-analysis. American Journal of Obstetrics & Gynecology MFM, 2(3), 100117.

Royal Australian and New Zealand College of Obstetricians and Gynaecologists. (2025). Vasa praevia (C-Obs 47, Clinical Guideline Version 3).

Sullivan, E. A., Javid, N., Duncombe, G., Li, Z., Safi, N., Cincotta, R., Homer, C. S. E., Halliday, L., & Oyelese, Y. (2017). Vasa previa diagnosis, clinical practice, and outcomes in Australia. Obstetrics & Gynecology, 130(3), 591–598.

Zhang, W., Geris, S., Al-Emara, N., Ramadan, G., Sotiriadis, A., & Akolekar, R. (2021). Perinatal outcome of pregnancies with prenatal diagnosis of vasa previa: Systematic review and meta-analysis. Ultrasound in Obstetrics & Gynecology, 57(5), 710–719.

Zhang, W., Giacchino, T., Chanyarungrojn, P. A., Ionescu, O., & Akolekar, R. (2023). Incidence of vasa praevia: A systematic review and meta-analysis. BMJ Open, 13(9), e075245.

Content Disclaimer

The information provided on this website is for educational and informational purposes only. It is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your obstetrician or other qualified provider for any questions you may have regarding a medical condition or treatment, and before undertaking a new healthcare regimen.

The content on this website is not intended to be a comprehensive source of information on any particular topic and should not be relied upon as such. The authors and publishers of this website are not liable for any damages or injury resulting from the use or misuse of the information provided on this website.

Cervical Insufficiency in Pregnancy: What It Is, How It’s Found, and What It Means

by Ben Sweetlove | Sep 15, 2026 | Pregnancy, QUFW News

If you have been told you have cervical insufficiency, it is natural to want to understand what it means for the rest of your pregnancy.

Here is some reassurance: cervical insufficiency is not something you have caused, and it is not a verdict on your pregnancy. It is a recognised and manageable condition, and your team monitors it closely so they can act early if needed. With monitoring and a clear plan in place, most women in this situation go on to have a healthy baby.

This article explains what cervical insufficiency is, how it is diagnosed, the scan used to check your cervix, and what a diagnosis means for the rest of your pregnancy.

Table of contents

1. What is cervical insufficiency?
2. How is cervical insufficiency diagnosed?
3. The scan used to check your cervix
4. Is cervical insufficiency the same as a short cervix?
5. What cervical insufficiency means for the rest of your pregnancy
6. Book a cervical assessment at QUFW
7. Frequently asked questions

What is cervical insufficiency?

The cervix is the lower part of the uterus, the passage that connects the uterus to the vagina. For most of your pregnancy, it is meant to stay firm and closed, holding everything safely in place until your body is ready for labour.

Cervical insufficiency describes a cervix that begins to open too early, usually during the second trimester, and often without the pain or contractions you would expect with labour. It can happen quietly and can lead to a very early birth or a mid-trimester loss.

Cervical insufficiency is more common in patients who have had previous cervical surgery or biopsy (such as a cone biopsy or a LLETZ procedure), prior early pregnancy loss or previous cervical insufficiency.

How is cervical insufficiency diagnosed?

No single test diagnoses cervical insufficiency on its own. It is largely a clinical diagnosis, meaning your obstetrician puts together several pieces of information rather than relying on a single result.

Your obstetric and gynaecological history is one of the most important clues. A previous painless loss in the second trimester, or a very early birth, is the classic situation that raises the possibility of cervical insufficiency. In a current pregnancy, it may also be suspected if an examination finds that the cervix has already begun to open, or if changes are seen when your cervix is assessed on ultrasound. Where your history or risk factors suggest an increased risk, your team will usually keep a close eye on your cervix through the pregnancy so that any change is picked up early.

When is the cervix checked?

The cervix is checked and measured routinely at all pregnancy scans. Patients will be asked to present to their pregnancy scans with a comfortably full bladder. A full bladder provides an acoustic window that allows your sonographer to adequately visualise the cervix. A cervical length measuring less than 35 mm on transabdominal ultrasound will prompt your sonographer to offer a transvaginal ultrasound for a more detailed assessment. This will only be performed with your consent. A transvaginal ultrasound is the preferred and most accurate method of measuring the cervix at the morphology scan (20-22 weeks). The examination is performed with an empty bladder and minimal pressure from the transducer. A transvaginal scan lasts no more than a minute or two. Some women feel apprehensive about having a transvaginal scan in pregnancy. This technique is safe in pregnancy, and most patients find it involves little or no discomfort. When there is a reason to monitor your cervix, these scans are usually repeated at different stages of pregnancy. This is exactly the kind of careful, specialist assessment where subspecialist experience and high-end equipment make a real difference.

Cervical insufficiency on ultrasound

Is cervical insufficiency the same as a short cervix?

These two terms are closely related, but not the same.

It is quite normal for the cervix to shorten slightly, but remain closed, toward the end of a pregnancy. The cervix is “short” when it measures less than 25 mm on transvaginal ultrasound. The cervix can remain short and closed until the onset of labour. A short cervix is more concerning the earlier it presents in pregnancy. For most patients, it is an isolated finding that is simply monitored with ultrasound at regular intervals. Your obstetrician will interpret your situation in the context of your full history and may prescribe progesterone.

A short cervix can progress to cervical insufficiency in some cases. Cervical insufficiency is when the cervix opens prematurely, allowing the amniotic membrane to protrude into the opening. In these cases, patients are more likely to experience premature rupture of membranes (PPROM), leading to premature delivery. These patients are more at risk of infection and early pregnancy loss.

What cervical insufficiency means for the rest of your pregnancy

The good news is that cervical insufficiency is actively managed, and you will not be navigating it alone.

In practice, your care will usually include closer monitoring of your cervix during the relevant weeks of pregnancy, so that any changes are picked up early. Alongside that, there are two main treatments. One option is a cervical cerclage: a stitch placed in the cervix to give it extra support. This may be recommended in certain situations, particularly where there is a history of a previous early loss or preterm birth. Another option is vaginal progesterone, usually taken nightly. There is good evidence that supports the use of progesterone to help reduce the risk of preterm birth in people with a short cervix by supporting uterine relaxation and limiting inflammatory changes that can contribute to cervical shortening. Cervical pessaries have been used to support a short or insufficient cervix, but evidence of the benefit is inconsistent, so they are not routinely recommended for preventing preterm birth. Vaginal progesterone and, in selected cases, cervical cerclage have stronger guideline support. Your obstetrician will advise you on the most appropriate approach and intervention based on your history and your individual circumstances.

Your team may also discuss whether to adjust certain activities, and this is a conversation worth having with them directly rather than relying on general advice. The most useful thing you can do is keep the lines of communication open with your team and ask them anything that is worrying you. Closer monitoring is not a sign that something is already wrong; it is a deliberate way of staying a step ahead.

Book a cervical assessment at QUFW

At QUFW, our consultants are subspecialist obstetricians and gynaecologists with extensive experience in obstetric ultrasound, supported by highly trained sonographers. If your history means your cervix needs close monitoring, we can provide the detailed transvaginal assessment needed to evaluate it accurately and support you and your care team with a clear plan forward.

If you would like to arrange an assessment, click here to book an appointment. We are here for you.

Frequently asked questions

Is cervical insufficiency the same as a short cervix?

Not quite. A short cervix is a measurement found on a scan and a risk marker. Cervical insufficiency is a diagnosis describing a cervix that opens too early, usually painlessly, in the second trimester. A short cervix can point toward that risk, but the two are not the same thing.

How is cervical insufficiency diagnosed?

Mainly from your history. Particularly a previous painless second-trimester loss or very early birth. This history, together with a clinical examination and a transvaginal ultrasound of the cervix, can help your care team make a diagnosis. No single test diagnoses it on its own; your obstetrician considers the full picture.

Can you have a successful pregnancy with cervical insufficiency?

Yes. With monitoring and a clear plan. This may include a cervical stitch or progesterone, and most women go on to have a healthy baby. Cervical insufficiency increases the chance of an early birth, but it does not determine the outcome.

Does cervical insufficiency have symptoms?

Often not, which is why the cervix is checked on a scan rather than by waiting for signs. Some women may notice pelvic pressure, backache, or a change in discharge, but these are non-specific and cannot be relied on. If you have any bleeding, fluid loss, or regular tightening, contact your care team promptly.

How is cervical insufficiency treated?

The two main options are a cervical stitch (cerclage) and vaginal progesterone, chosen according to your circumstances and history, alongside closer monitoring of your cervix. Your obstetrician will recommend the approach best suited to you.

Sources: This article draws on guidance from the Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG). For more, see the RANZCOG resource hub at ranzcog.edu.au/resource-hub.

Content Disclaimer

The information provided on this website is for educational and informational purposes only. It is not intended as a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your obstetric doctor or other qualified provider with any questions you may have about a medical condition or treatment, and before starting a new healthcare regimen.

The content on this website is not intended to be a comprehensive source of information on any particular topic and should not be relied upon as such. The authors and publishers of this website are not liable for any damages or injury resulting from the use or misuse of the information provided on this website.