Placenta Previa – all about the complication

By Dr Rosemary Listing, PhD (Product Liability), Of Counsel, Peter Evans & Associates | Birth trauma and obstetric negligence | Reading time: about 12 minutes

Placenta praevia is one of the most serious placental conditions in pregnancy. It occurs when the placenta implants low in the uterus and covers, or sits very close to, the cervix. Most people first hear the words "low-lying placenta" at their 18 to 20 week morphology scan. For the large majority, the placenta moves up and the pregnancy continues normally. For a smaller group, the placenta stays low. That can lead to sudden bleeding, an early caesarean, a blood transfusion and, in the most severe cases, an emergency hysterectomy.

This guide explains which earlier pregnancy complications and procedures increase the risk of placenta praevia, how the condition can cause problems at birth for both mother and baby, and when poor management may amount to medical negligence under NSW law. It is written for families, not clinicians. It does not replace advice from your doctor or midwife.

What is placenta praevia?

The placenta grows with your baby and attaches to the wall of the uterus. It delivers oxygen and nutrients from your bloodstream to your baby. Normally it attaches towards the top or side of the uterus. In placenta praevia, it attaches in the lower part of the uterus, over or beside the cervix, which is the exit your baby needs for a vaginal birth.

The Royal College of Obstetricians and Gynaecologists (RCOG) uses two terms in its patient information on placenta praevia, placenta accreta and vasa praevia:

• Low-lying placenta: the placental edge is less than 20 mm from the cervix after 16 weeks.
• Placenta praevia: the placenta lies directly over the internal os (the inner opening of the cervix).

You may also see the older terms "minor" and "major" placenta praevia, or the American spelling "placenta previa". NSW hospital guidelines, such as the South Eastern Sydney Local Health District placenta praevia and low-lying placenta guideline, use the same distinction between a placenta that covers the os and one that sits within 2 cm of it.

How common is it?

A low-lying placenta at the morphology scan is common, but it usually resolves. According to the RCOG, around 9 in 10 women with a low-lying placenta at 20 weeks no longer have one at their follow-up scan. Only about 1 in 200 women overall will still have placenta praevia at the end of pregnancy. The placenta does not physically move. Instead, the lower segment of the uterus stretches and grows as pregnancy advances, which carries the placental edge upwards.

This "upward migration" is less likely if you have had a previous caesarean. A scar in the lower uterus can anchor the placenta and change how it attaches. This is one reason a caesarean history matters so much.

What causes placenta praevia? Complications and procedures that increase the risk

Doctors do not fully understand why the placenta implants low in some pregnancies. The common thread in the research is damage or scarring to the lining of the uterus (the endometrium). When the upper uterus is less receptive, the placenta may implant lower, where blood supply and tissue conditions suit it better. The following factors are consistently linked with a higher risk.

1. A previous caesarean section

A previous caesarean is the single most important modifiable risk factor. The risk increases with each caesarean. The RCOG notes that placenta praevia is more common after one or more caesarean births. The combination of a caesarean scar and a low placenta is also the main pathway to placenta accreta spectrum (discussed below). If you are weighing up birth options in a future pregnancy, our guide to caesarean rates, safety and your legal rights explains why these long-term risks should be part of the consent conversation.

2. Other surgery on the uterus

Any procedure that disturbs the uterine lining can increase the risk. This includes:

• dilatation and curettage (D&C), including repeated curettage
• surgical management of miscarriage or termination of pregnancy
• myomectomy (surgical removal of fibroids)
• manual removal of a retained placenta in a previous birth
• hysteroscopic surgery on the uterine cavity

3. A previous placenta praevia

If you have had placenta praevia before, you are more likely to have it again. Your antenatal team should record this history at booking and plan scanning accordingly.

4. IVF and other assisted reproduction

The RCOG lists fertility treatment as a risk factor for placenta praevia. IVF pregnancies also carry a higher risk of placenta accreta.

5. Older maternal age and multiple previous births

Pregnancy, Birth and Baby (Healthdirect) identifies maternal age, twin or multiple pregnancy and past caesareans as factors that affect the risk. Having had several previous births (multiparity) is also associated with a higher risk.

6. Twin or multiple pregnancy

A larger placenta, or two placentas, covers more of the uterine wall, which increases the chance that part of it lies low.

7. Smoking and drug use

Smoking during pregnancy is a recognised risk factor. Cocaine use is also associated with placenta praevia in the medical literature.

8. Uterine abnormalities

Fibroids and an unusually shaped uterus (such as a bicornuate uterus) can affect where the placenta implants. The RCOG notes these are also risk factors for placenta accreta.

How is placenta praevia diagnosed?

Placenta praevia is diagnosed by ultrasound. In Australia, placental location is assessed at the routine morphology scan at about 18 to 20 weeks. The RCOG guidance, which Australian hospitals commonly draw on, recommends:

• a follow-up scan at about 32 weeks if the placenta is low-lying or praevia at 20 weeks
• a transvaginal ultrasound to confirm the diagnosis, because it is more accurate than an abdominal scan and is safe in placenta praevia
• a further scan at about 36 weeks if the placenta is still low at 32 weeks, to finalise the plan for birth

The full clinical recommendations are in the RCOG's Green-top Guideline No. 27a: Placenta Praevia and Placenta Accreta.

Warning signs

The classic symptom is painless vaginal bleeding, usually after 28 weeks. Bleeding can happen after sex, or with no trigger at all. It may be light, or sudden and heavy. Some people have no symptoms until labour begins. Placenta praevia may also be suspected if the baby is breech or lying sideways (transverse) late in pregnancy. The Better Health Channel notes the baby is in one of these positions in around one in three cases.

If you know you have a low-lying placenta and you notice any bleeding, contractions or abdominal pain, go to hospital immediately. Do not wait to see whether it settles. If you feel your concerns were dismissed, our article on when being dismissed by a doctor becomes a legal issue may help.

How placenta praevia causes problems at birth

When the placenta lies over the cervix, it blocks the baby's exit. As the cervix softens and opens in late pregnancy or labour, the placenta can tear away from the uterine wall and bleed heavily. Because the lower segment of the uterus does not contract as strongly as the upper uterus, bleeding from the placental site can also be harder to stop after birth.

The birth plan: why a caesarean is usually needed

The RCOG advises that if the placental edge is less than 20 mm from the cervix on the 36-week scan, a caesarean is the safest way to give birth. If there has been no significant bleeding, the caesarean is usually planned for 36 to 37 weeks. If you have bled, it may need to happen earlier. The RCOG also recommends that a senior obstetrician and anaesthetist be present, that blood be available, and that the birth take place in a hospital equipped to manage heavy bleeding.

Where the placenta is more than 20 mm from the cervix, a vaginal birth may be a reasonable choice after discussion with your care team.

Complications for the mother

Placenta accreta spectrum: the most dangerous complication

Placenta accreta spectrum (PAS) occurs when the placenta attaches too deeply. There are three grades:

• placenta accreta, where it attaches firmly to the uterine muscle
• placenta increta, where it grows into the muscle
• placenta percreta, where it grows through the uterus and may reach the bladder or other organs

Because the placenta cannot separate, any attempt to pull it away can cause catastrophic bleeding. The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (RANZCOG) Placenta Accreta Spectrum (C-Obs 20) clinical guideline identifies four independent risk factors for Australian and New Zealand women: previous caesarean, placenta praevia diagnosed before birth, older maternal age and multiparity. The national data behind that guideline, published in BMJ Open (Farquhar et al, 2017), found placenta praevia was by far the strongest predictor of placenta accreta.

The risk compounds with each caesarean. A review of placenta accreta spectrum reports that a woman with placenta praevia and three previous caesareans has a 61% risk of PAS.

The RANZCOG guideline recommends that every woman with a probable or confirmed PAS diagnosis be reviewed by a multidisciplinary team with expertise in complex pelvic surgery. That team should plan the place of birth, ensuring on-site transfusion services and adult and neonatal intensive care. The guideline also notes that women in rural and regional areas may face higher risk, and that early relocation or retrieval may need to be considered. Antenatal diagnosis is what makes this planning possible, so the quality of the scans matters.

Complications for the baby

Preterm birth

Bleeding often forces an early birth, and even uncomplicated placenta praevia usually leads to a planned caesarean at 36 to 37 weeks. Babies born early may need breathing support, a stay in neonatal intensive care, and help with feeding and temperature control. The RCOG recommends offering antenatal corticosteroids between 34 and 36 weeks to help mature the baby's lungs.

Oxygen deprivation and brain injury

When the mother loses a large volume of blood, blood flow to the placenta falls. A severe or prolonged haemorrhage can starve the baby of oxygen. This may cause hypoxic-ischaemic encephalopathy (HIE), cerebral palsy or, tragically, stillbirth. How quickly the team recognises the haemorrhage and delivers the baby is often critical to the outcome.

Abnormal position

Because the placenta occupies the lower uterus, the baby's head often cannot settle into the pelvis. Breech and transverse positions are more common.

Vasa praevia

A low-lying placenta is one of the risk factors for vasa praevia. In this condition, unprotected fetal blood vessels run across or near the cervix. If they tear when the waters break, the baby bleeds directly, and the RCOG estimates up to 6 in 10 affected babies can die. When vasa praevia is diagnosed before labour, a planned caesarean at around 34 to 36 weeks is recommended. See the RCOG's Green-top Guideline No. 27b on vasa praevia.

If you noticed your baby moving less before a bleed or before birth, please read our guide on reduced foetal movements late in pregnancy. Reduced movements always warrant same-day assessment.

When does placenta praevia become a medical negligence issue?

Placenta praevia is a recognised complication of pregnancy. A poor outcome, even a devastating one, does not by itself mean care was negligent. What the law examines is whether the clinicians caring for you acted as a reasonably competent practitioner would have in the same circumstances, and whether any failure caused harm that would otherwise have been avoided.

In our experience, harm in placenta praevia cases is rarely the result of one dramatic moment. It is more often a chain of missed opportunities, each of which narrowed the margin for safety. Examples we look for include:

Failures in scanning and follow-up

• The morphology scan reported a low-lying placenta, but nobody arranged the follow-up scan.
• The report was filed without being read or acted on, or was never communicated to the woman.
• Placental position was not properly assessed in a woman with a previous caesarean.
• A transabdominal scan was relied on when a transvaginal scan was needed to clarify the position.
• The scan did not consider placenta accreta, despite placenta praevia plus a caesarean scar.

These can be framed as delayed or missed diagnosis claims.

Failures in birth planning

• Birth was planned in a hospital without blood bank, theatre or intensive care capacity appropriate to the risk.
• No multidisciplinary planning occurred for suspected placenta accreta spectrum.
• A senior obstetrician and anaesthetist were not involved in a high-risk caesarean.
• Cross-matched blood was not available at the time of surgery.
• Women in regional or remote areas were not relocated in time.

Failures in responding to bleeding

• A woman with known placenta praevia was sent home after a bleed without adequate assessment.
• A digital vaginal examination was performed in a woman with an unknown or known low placenta, triggering haemorrhage. A speculum examination is the accepted approach in this setting.
• Escalation to a senior doctor, or transfer to theatre, was delayed once heavy bleeding began.
• Blood loss was underestimated, or postpartum haemorrhage protocols were not followed.
• Fetal heart rate monitoring was not commenced or acted on during a bleed.

Failures of informed consent

Women with placenta praevia, particularly those at risk of accreta, should be told about the realistic possibility of transfusion, hysterectomy and injury to nearby organs before surgery. In Australia, the leading case on the duty to warn is Rogers v Whitaker (1992) 175 CLR 479. It requires doctors to disclose material risks: those a reasonable person in the patient's position would consider significant, or that the doctor knows this particular patient would. Consent concerns arise across obstetric care. Our story Emily's triumph after an unconsented episiotomy shows how this plays out in practice.

The legal framework in NSW

The standard of care

Medical negligence claims in NSW are governed by the Civil Liability Act 2002 (NSW). Section 5O provides a defence where a professional acted in a manner widely accepted in Australia by peer professional opinion as competent practice. A court can reject that opinion if it is irrational. In practice, this means independent expert evidence from experienced obstetricians, and often from sonographers, haematologists and neonatologists, is central to any claim.

Time limits

Under section 50C of the Limitation Act 1969 (NSW), a claim for personal injury generally must be brought within three years from the date the claim is "discoverable", and no later than 12 years from the act or omission. Discoverability depends on when you knew, or ought to have known, that an injury occurred, that it was caused by fault, and that it was serious enough to justify a claim. The NSW Civil Trials Bench Book on limitation periods explains how courts apply these rules. Different rules can apply to children injured at birth. Our articles on NSW medical negligence time limits and whether you can still sue years later explain the detail.

What you may be able to claim

A successful claim may compensate for pain and suffering, medical and rehabilitation costs, lost income, care provided by family, and future needs. For a child with a birth-related brain injury, those future needs can be lifelong. For a mother who lost her uterus, the claim may include the loss of future fertility. Many families also face financial strain while they recover. We discuss this in medical negligence and financial debt in NSW.

What to do if you think something went wrong

1. Ask for an open disclosure meeting. Australian health services must have an open disclosure program consistent with the Australian Open Disclosure Framework. This means an honest discussion about what happened and why.
2. Request your records. Ask for your full maternity file, including ultrasound reports and images, CTG traces, operation notes, anaesthetic records, blood bank records and your baby's neonatal records.
3. Write down your timeline while it is fresh. Record when bleeding started, who you spoke to, what you were told, and how long each step took.
4. Consider a complaint. You can raise concerns with the NSW Health Care Complaints Commission. A complaint is separate from a compensation claim and does not replace one.
5. Get legal advice early. Time limits apply, and evidence such as scan images is easier to secure sooner.

How we can help

Dr Rosemary Listing works exclusively for injured patients and families. She focuses on birth trauma and obstetric negligence. Her approach maps every decision point in your care, from the first scan to the postnatal ward. The aim is to identify where care fell short, not just where the outcome went wrong. She also delivers informed-consent training to maternity clinicians, including birth trauma training with the Maternity Consumer Network. That work gives her a clear view of how consent and escalation should work on a busy birth suite.

You can read more about Dr Listing, browse our resource hub, or read one family's experience in Ms Jones' fight for justice after birth trauma.

Frequently asked questions about placenta praevia

Sources

• Royal College of Obstetricians and Gynaecologists, Placenta praevia, placenta accreta and vasa praevia (patient information, 2018)
• RCOG, Green-top Guideline No. 27a and No. 27b
• RANZCOG, Placenta Accreta Spectrum (C-Obs 20) clinical guideline
• Farquhar CM et al, Incidence, risk factors and perinatal outcomes for placenta accreta in Australia and New Zealand, BMJ Open 2017
• Placenta Accreta Spectrum: A Review of Pathology, Molecular Biology, and Biomarkers (2018)
• South Eastern Sydney LHD, Placenta praevia / low-lying placenta guideline
• Precise mid-trimester placenta localisation: does it predict adverse outcomes? ANZJOG 2012
• Healthdirect, Pregnancy, Birth and Baby: Placenta praevia
• Victorian Department of Health, Better Health Channel: Placenta praevia

This article provides general information only. It is not medical or legal advice and should not be relied on as a substitute for advice about your circumstances. Reframe Legal is a thought leadership website by Dr Rosemary Listing. Legal services are provided by Peter Evans & Associates. Liability limited by a scheme approved under Professional Standards Legislation.