The placenta normally attaches to the upper part of the uterus. When it lies low and covers, or sits close to, the cervix, it is called placenta praevia or a low-lying placenta. Because the cervix opens in labour, a placenta in this position can bleed, sometimes heavily, and usually means the baby is born by caesarean. Placenta praevia affects about 1 in 200 pregnancies at term.
In placenta accreta spectrum (PAS), the placenta grows too deeply into the wall of the uterus and does not separate after birth. Its strongest risk factor is a previous caesarean combined with a low placenta lying over the old scar, and the risk climbs steeply with each additional caesarean. With caesarean rates rising across India, PAS is seen more often than it was a generation ago.
Dr. Devang Patel, trained in maternal-fetal medicine at Fernandez Hospital, Hyderabad, assesses placental position and attachment on scan and plans delivery for these pregnancies at Divine Women’s Hospital, Gota, Ahmedabad, where 24×7 emergency and labour care is available if bleeding starts unexpectedly.
Low-lying placenta, praevia and accreta: the terms
Scan reports use several terms that sound similar but mean quite different things. The measurement that matters is the distance between the placental edge and the internal opening of the cervix, measured most accurately on a transvaginal scan, which is safe even when the placenta is low.
| Finding | What it means | Usual implication |
|---|---|---|
| Low-lying placenta | Edge within 20 mm of the cervix after 16 weeks | Often moves up; vaginal birth possible if more than 20 mm away at the final scan |
| Placenta praevia | Placenta covers the internal opening of the cervix | Planned caesarean if it persists in the third trimester |
| Placenta accreta | Placenta attached abnormally firmly to the muscle | Does not separate; risk of heavy bleeding at birth |
| Placenta increta | Placenta grows into the muscle wall | Usually needs major surgery, often hysterectomy |
| Placenta percreta | Placenta grows through the uterus, sometimes into the bladder | Complex multi-team surgery at a centre with full backup |
Why a low placenta often moves up
A low placenta is reported in a few per cent of anomaly scans at 18–22 weeks. In about nine out of ten of these women it no longer covers the cervix by the third trimester. The placenta does not actually travel; the lower part of the uterus grows and stretches much more than the rest, carrying the placental edge upwards.
This is why a low placenta at 20 weeks is not a reason for alarm or for strict rest. A follow-up transvaginal scan is arranged at about 32 weeks, and again at about 36 weeks if it is still low and you have had no bleeding. Women with a previous caesarean and a low anterior placenta are an exception: they need a focused scan for accreta signs.
Who is at risk
- One or more previous caesareans, especially with a low placenta now lying over the scar
- Previous surgery on the uterus, such as myomectomy, hysteroscopic surgery or repeated D&C
- Pregnancy after IVF
- Maternal age over 35 and several previous births
- Smoking or tobacco use
- A previous placenta praevia or accreta
With a placenta praevia over the scar, the chance of accreta is roughly 3% after one previous caesarean, about 11% after two, and around 40% after three.
Symptoms: the typical pattern of bleeding
Placenta praevia classically causes bright red vaginal bleeding without pain, often in the third trimester and sometimes after intercourse or for no clear reason. The first bleed is frequently small and stops on its own, but later bleeds can be heavier, so every episode needs assessment in hospital.
Placenta accreta usually causes no symptoms at all during pregnancy. It is suspected because of risk factors and scan findings, and confirmed at delivery. Rarely, percreta into the bladder causes blood in the urine.
A related condition, vasa praevia, is worth knowing about. Here, unprotected fetal blood vessels run across the cervix, often with a low placenta or after IVF. It is looked for with colour Doppler on a transvaginal scan, because if it is found, a planned caesarean before labour protects the baby.
How accreta is diagnosed before birth
Experienced ultrasound is the main tool. Signs include loss of the clear zone between placenta and uterine wall, irregular blood-filled spaces (lacunae) within the placenta, thinning of the uterine muscle over the scar, and abnormal blood vessels at the bladder surface on colour Doppler. In the first trimester, a pregnancy implanted low on the caesarean scar can be an early warning.
MRI is sometimes added for a placenta at the back of the uterus or to map how far invasion extends. Neither test is perfect, so when suspicion is high, planning proceeds as if accreta is present. The point of antenatal diagnosis is that the right team, blood products and setting are arranged before the day of delivery rather than in an emergency.
Precautions during pregnancy
- Come to the hospital for any vaginal bleeding, even light spotting without pain
- Avoid intercourse and internal examinations when the placenta is praevia
- Keep haemoglobin above 11 g/dL with iron, and intravenous iron if tablets are not enough, so you start with reserves if bleeding occurs
- Know your blood group; if you are Rh-negative, anti-D is given after a bleed
- Steroid injections are given if early delivery looks likely before 35 weeks
- Stay within easy reach of the hospital in the third trimester, with an adult and transport available at all times
- Strict bed rest is not routinely advised, as it raises the risk of blood clots; some women with repeated bleeds are admitted for observation
Planning the delivery
Uncomplicated placenta praevia is usually delivered by planned caesarean between 36 and 37 weeks. Suspected accreta is usually delivered a little earlier, between 35 and 36+6 weeks, as a scheduled operation with senior obstetric and anaesthesia teams present, blood cross-matched in advance, and medicines such as tranexamic acid and uterotonics ready.
For accreta, the operation is often a caesarean hysterectomy with the placenta left in place, which is the most reliable way to control bleeding. In selected women, conservative approaches are considered. For suspected percreta or bladder involvement, delivery is planned at a tertiary centre with urology, interventional radiology and intensive care backup, and this referral is discussed openly with you.
Recovery and future pregnancies
Recovery after a planned praevia caesarean is similar to any caesarean, with a hospital stay of two to four days. After accreta surgery, recovery takes longer, and blood transfusion is more often needed. Clot-prevention injections, early walking and iron replacement are part of aftercare.
After placenta praevia, the chance of it recurring is raised. After a caesarean hysterectomy for accreta, further pregnancy is not possible, and the emotional impact of this is acknowledged and supported. Where the uterus has been conserved, a future pregnancy needs early scanning to check where the placenta implants.
The most effective long-term prevention of accreta is avoiding caesareans that are not medically needed, especially in a first birth.
Your care, step by step
- Placental mappingTransvaginal and colour Doppler scans define where the placenta lies and whether there are signs of abnormal attachment.
- Follow-up scansRepeat scans at about 32 and 36 weeks show whether the placenta has moved away from the cervix.
- Bleeding readinessAnaemia is corrected, your blood group is on record and you know exactly when and how to reach the hospital.
- Team planningFor suspected accreta, timing, anaesthesia, blood products and, if needed, tertiary referral are agreed in advance.
- Scheduled delivery and aftercarePlanned caesarean with neonatal support, followed by recovery, iron and clot prevention.
When to book a visit
- Your scan report says low-lying placenta, placenta praevia or suspected accreta
- You have had one or more caesareans and are pregnant again
- An early scan suggests the pregnancy is implanted low on a caesarean scar
- You had uterine surgery such as myomectomy before this pregnancy
- You conceived through IVF and the placenta is reported as low
- You want to plan travel, work or an out-of-town stay with a low placenta
Warning signs - get same-day care
- Any vaginal bleeding in the second half of pregnancy, even if light and without pain
- Heavy bleeding, passing clots, or feeling faint or dizzy
- Bleeding with abdominal pain or a hard, tender uterus
- Contractions or waters breaking when you know the placenta is low
- Reduced baby movements after a bleed
Labour and emergency care are available 24 × 7. Call the hospital and come in directly.
Myths and facts
Myth: A low placenta at 20 weeks means I will definitely need a caesarean.
Most low placentas move well away from the cervix by the third trimester. The decision is made after the 32–36 week scan.
Myth: An internal scan will cause bleeding when the placenta is low.
A gentle transvaginal scan is safe with placenta praevia and gives a more accurate measurement than an abdominal scan.
Myth: Complete bed rest keeps the placenta from bleeding.
Strict bed rest has not been shown to prevent bleeding and increases the risk of blood clots. Avoiding intercourse and heavy exertion and staying near the hospital matter more.
Myth: If the first bleed stopped on its own, there is nothing to worry about.
A first bleed is often small, but later bleeds can be heavier. Every episode needs assessment, and the delivery plan may change after it.
Frequently asked questions
Can a low-lying placenta move up?
Yes, in most cases. As the lower part of the uterus grows, the placental edge usually ends up well away from the cervix by the third trimester. A repeat scan at about 32 weeks is arranged before any decision about delivery.
Can I have a normal delivery with placenta praevia?
If the placenta still covers the cervix late in pregnancy, a caesarean is needed. If it is low-lying but more than 20 mm from the cervix at the final scan, a vaginal birth can often be considered.
Is placenta praevia dangerous for the baby?
The main risk to the baby is being born early if bleeding forces delivery. With steroid injections when early birth is likely and planned neonatal support, most babies do well.
Should I take complete bed rest?
Strict bed rest is not routinely advised, as it raises the risk of blood clots without clear benefit. Avoid heavy work and intercourse, stay close to the hospital, and come in promptly if you bleed.
What is placenta accreta and is it dangerous?
It is a condition where the placenta grows into the wall of the uterus and does not come away after birth, which can cause heavy bleeding. It is serious, but when it is recognised before delivery and the operation is planned with the right team, outcomes are much better.
How is placenta accreta detected on ultrasound?
Signs include loss of the normal clear zone behind the placenta, irregular spaces inside the placenta, a thin uterine wall over the scar and abnormal vessels near the bladder on colour Doppler. MRI is added in selected cases.
Will I need a hysterectomy if I have placenta accreta?
Often a hysterectomy at the time of caesarean is the most reliable way to control bleeding in accreta spectrum. In selected cases conservative options may be possible. The likely approach and what it means for future pregnancies is discussed in detail beforehand.
I have had two caesareans. Am I at risk of accreta?
Your risk is higher than average, mainly if the placenta is low and lies over the scar. A focused scan of the scar area is arranged, often from the first trimester, so that any concern is identified early.
Is it safe to travel or work with placenta praevia?
Desk work and short local travel are usually fine in the second trimester if you have had no bleeding. In the third trimester, avoid long journeys and places far from a hospital, and do not travel alone.
What happens if I bleed with placenta praevia?
You are assessed straight away: your pulse, BP and the amount of bleeding are checked, the baby is monitored, blood is taken for haemoglobin and cross-match, and anti-D is given if you are Rh-negative. Most bleeds settle and you are observed for at least a day or two; heavy or continuing bleeding may mean the baby has to be delivered, whatever the gestation.