Placenta Previa: Symptoms, Causes, Diagnosis & Delivery
Placenta Previa: Symptoms, Causes, Diagnosis & Delivery
Placenta previa is a pregnancy condition in which the placenta lies unusually low in the uterus and may partially or completely cover the cervix, the opening through which the baby would normally be born.
It is an important condition because a low-lying placenta can cause vaginal bleeding during the second half of pregnancy, sometimes suddenly and heavily. When the placenta continues to cover the cervix near the end of pregnancy, a caesarean birth is usually recommended.
However, being told that your placenta is low at the 20-week ultrasound does not necessarily mean you will have placenta previa at delivery. As the uterus grows, the placenta often ends up farther away from the cervix.
These terms are related but slightly different.
Low-lying placenta: the lower edge of the placenta is close to the cervix, generally within 20 mm (2 cm).
Placenta previa: the placenta covers the cervix.
A placenta that is low at the mid-pregnancy scan may move away from the cervix as pregnancy progresses. RCOG notes that most women with a low-lying placenta at the 20-week scan will no longer have a low-lying placenta at follow-up.
This is why the position of the placenta later in pregnancy is more important when planning delivery.
In many cases, there is no single identifiable cause.
Certain factors are associated with a higher chance of placenta previa, including:
Previous caesarean delivery
Previous surgery on the uterus
Multiple pregnancy, such as twins
Fertility treatment, including IVF
Smoking
Increasing maternal age
Previous placenta previa
A particularly important association is previous caesarean delivery. If the placenta is low and lies over a previous caesarean scar, doctors may also assess for placenta accreta spectrum, where the placenta grows abnormally deeply into the uterine wall.
The most typical symptom is:
The bleeding may occur suddenly and can sometimes be heavy.
However, not every woman with placenta previa has bleeding before delivery.
Bleeding can also occur after sex, and some women may have contractions or abdominal discomfort. Therefore, any vaginal bleeding during pregnancy should be assessed promptly rather than assuming that it is simply due to placenta previa.
If you have been told that you have a low-lying placenta or placenta previa, contact your maternity hospital or obstetrician immediately if you develop vaginal bleeding, contractions or pain. Heavy bleeding during pregnancy can be an emergency.
How is placenta previa diagnosed?
The position of the placenta is usually assessed during the routine mid-pregnancy ultrasound, commonly around 18–22 weeks.
If the placenta appears close to the cervix, your doctor may recommend a follow-up ultrasound later in pregnancy.
A transvaginal ultrasound may be used to determine the exact distance between the placenta and cervix. Despite the name, this is considered a safe way to assess placental position when medically indicated.
Follow-up timing depends on the initial findings and your individual circumstances. A commonly used approach is reassessment around 32 weeks and, if the placenta remains low, again around 36 weeks.
The placenta does not literally move from one part of the uterus to another.
Instead, as the uterus expands during pregnancy, the relationship between the placenta and cervix changes. A placenta that appears low earlier in pregnancy may therefore be farther from the cervix later.
This is why a diagnosis of a low-lying placenta at the 20-week scan does not automatically mean placenta previa at delivery.
There is no exercise, food or home remedy proven to “move” the placenta upwards.
It can.
When the placenta occupies the lower part of the uterus, the baby may be more likely to remain in an unusual position, such as breech or transverse lie.
This is one reason the baby's position and placental location are monitored as pregnancy progresses.
If the placenta continues to cover the cervix near term, vaginal delivery is generally not safe, because the placenta can obstruct the baby's passage and may bleed heavily when the cervix begins to open.
A planned caesarean birth is therefore usually recommended when placenta previa persists.
If the placenta is no longer covering the cervix and is sufficiently far away from it, vaginal birth may be possible depending on the individual situation. The exact decision is based on the placental position, bleeding history, pregnancy and clinical assessment.
For uncomplicated placenta previa, planned caesarean delivery is commonly scheduled around 36–37 weeks, although the exact timing is individualised.
If you have significant or recurrent bleeding, labour begins, your waters break, or there are other concerns about you or your baby, delivery may need to happen earlier.
The delivery should take place in a hospital equipped to manage significant obstetric bleeding, particularly when there are additional risk factors.
Placenta previa can be serious primarily because of the risk of major maternal bleeding.
Potential complications include:
Heavy vaginal bleeding
Anaemia
Preterm birth
Emergency caesarean delivery
Need for blood transfusion in severe bleeding
There is also an increased risk of placenta accreta spectrum, particularly when placenta previa occurs over a previous caesarean scar. Placenta accreta can cause severe bleeding during delivery and requires specialist planning.
This does not mean that every woman with placenta previa will develop placenta accreta.
Having placenta previa in one pregnancy does not mean you will definitely have it again. However, a previous placenta previa can increase the chance of placenta previa in a future pregnancy. The risk may also be higher after previous caesarean births or other uterine procedures. In a subsequent pregnancy, your obstetrician may pay particular attention to the placenta's location during routine ultrasound scans. If the placenta is found to be low-lying or covering the cervix, follow-up scans may be recommended to see whether its position changes as the uterus grows.
If you have a low-lying placenta, your antenatal care may include additional ultrasound scans to monitor its position.
Your doctor may also pay particular attention to:
Haemoglobin and iron levels
Episodes of vaginal bleeding
Baby's growth and wellbeing
Placental position
Baby's presentation
Signs of preterm labour
Features suggesting placenta accreta when relevant
If there is a significant risk of premature delivery, corticosteroids may be recommended to help reduce complications associated with prematurity. The decision and timing depend on gestational age and individual circumstances.
Placenta previa can be managed during pregnancy in India, but women with persistent placenta previa or significant bleeding should ideally deliver at a hospital with appropriate obstetric, anaesthesia, blood-bank/transfusion and newborn-care facilities.
If you have previously had a caesarean and your current ultrasound shows a low placenta, discuss this early with your obstetrician because the combination can increase concern for placenta accreta spectrum. Current international guidance also recognises that abnormal placental attachment can be associated with previous uterine procedures other than caesarean delivery.
If you have been diagnosed with placenta previa, don't wait for your next routine appointment if you develop any vaginal bleeding, contractions or significant pain.
Yes, a low-lying placenta diagnosed in the middle of pregnancy often ends up farther from the cervix as pregnancy progresses. However, persistent placenta previa later in pregnancy is less likely to resolve and requires careful delivery planning.
Placenta previa is primarily a condition of the second half of pregnancy and is more strongly associated with vaginal bleeding and preterm birth than early miscarriage. A low placenta seen early in pregnancy should not automatically be considered placenta previa.
Yes. Bleeding from placenta previa can lead to an unplanned early delivery, and some women require delivery before 37 weeks. The risk depends on factors such as bleeding episodes, gestational age and whether other complications are present.
Yes. Placenta previa can cause sudden and sometimes severe vaginal bleeding, particularly later in pregnancy. Heavy bleeding requires urgent medical assessment.
A placenta that is simply low-lying at the mid-pregnancy scan often becomes farther from the cervix as pregnancy progresses. Persistent placenta previa, especially when the placenta continues to cover the cervix later in pregnancy, usually requires planned caesarean delivery.
Sometimes. If the placenta is no longer covering the cervix and is sufficiently far away from it at the end of pregnancy, vaginal birth may be considered. If the placenta continues to cover the cervix, caesarean delivery is generally recommended.
No.
Placenta previa describes where the placenta is located in relation to the cervix.
Placenta accreta spectrum describes abnormal attachment of the placenta, where it grows too deeply into the uterine wall.
The two conditions can occur together, particularly when placenta previa is present over a previous caesarean scar, but they are different conditions.
The main concern is the risk of bleeding and preterm birth. If the mother experiences significant bleeding or needs early delivery, the baby may be affected by prematurity. With appropriate monitoring and delivery planning, many pregnancies with placenta previa can be managed safely.
Placenta previa means the placenta is lying very close to or covering the cervix. A low placenta seen at the mid-pregnancy ultrasound does not necessarily remain low until delivery.
The most important warning sign is vaginal bleeding, which may be painless and can sometimes be heavy. Persistent placenta previa near term usually requires a planned caesarean birth, while the exact timing depends on bleeding, pregnancy progress and other risk factors.
If you have been diagnosed with a low-lying placenta, keep your follow-up scans and contact your obstetrician promptly if you experience bleeding, contractions or pain