Placenta Praevia

Placenta praevia is a pregnancy complication where the placenta blocks the exit for the baby, affecting about 1 in 200 pregnancies and requiring careful management to protect both mother and child.

Table of contents

• What is placenta praevia?
• Types of placenta praevia
• Associated anatomy
• Symptoms
• Causes and risk factors
• How is it diagnosed?
• Possible complications
• Treatment and management
• Delivery options
• Living with placenta praevia
• Outlook

What is placenta praevia?

Placenta praevia is a condition during pregnancy when the placenta (the organ that provides oxygen and nutrients to the growing baby) attaches to the lower part of the uterus and covers all or part of the cervix (the opening to the birth canal)^[1][2]. During pregnancy, the placenta normally attaches to the top or side of the uterus, away from the cervix. This positioning allows the baby to exit through the cervix during birth^[3].

The placenta stretches and grows throughout pregnancy. It is common for the placenta to be positioned low in the uterus during early pregnancy. As the pregnancy progresses, particularly in the third trimester (weeks 28 to 40), the placenta usually moves toward the top of the uterus as the uterus expands. This movement creates a clear path for the baby to exit during delivery^[1][5].

When placenta praevia occurs, the placenta remains in a low position and blocks the baby’s exit route. This makes vaginal delivery dangerous because as the cervix opens during labor, it would separate the placenta from the uterine wall, causing severe bleeding and limiting the baby’s oxygen supply^[4][7].

Placenta praevia occurs in approximately 1 in 200 pregnancies^[1][5]. Many cases diagnosed early in pregnancy resolve on their own as the uterus grows. In fact, about 90% of early diagnoses correct themselves before delivery, meaning only about 1 in 800 pregnant women still have placenta praevia at the time of delivery^[13].

Types of placenta praevia

There are several types of placenta praevia, classified based on how much of the cervix the placenta covers^[1][3]:

• Marginal placenta praevia: The placenta is positioned at the edge of the cervix, touching it but not covering it. This type is more likely to resolve on its own before the baby’s due date^[1][7].
• Partial placenta praevia: The placenta partially covers the cervix^[1][14].
• Complete or total placenta praevia: The placenta completely covers the cervix, fully blocking the birth canal. This type is less likely to correct itself and presents the highest risk^[1][7].

Healthcare providers also distinguish between placenta praevia and a low-lying placenta. A low-lying placenta (sometimes called marginal placenta praevia) is near the cervix but within 2 centimeters of it without covering it^[13].

Associated anatomy

• Uterus
• Placenta
• Cervix
• Umbilical cord

Symptoms

The main symptom of placenta praevia is bright red, painless vaginal bleeding that typically begins after 20 weeks of pregnancy^[1][2][3]. The bleeding often starts near the end of the second trimester or the beginning of the third trimester. Sometimes spotting occurs first, followed by heavier bleeding episodes^[2].

The bleeding may stop on its own but can start again days or weeks later. In some cases, women may not experience any bleeding until labor begins^[3][8]. The amount of vaginal bleeding can vary greatly between individuals^[1].

Other symptoms may include^[1]:

• Mild cramping or contractions in the abdomen, belly, or back
• In some cases, there may be no symptoms at all, and the condition is only detected during routine ultrasound examinations^[13]

The bleeding can sometimes be triggered by sexual intercourse or during a medical examination^[2][4]. Any vaginal bleeding during pregnancy should be reported to a healthcare provider immediately, as it could indicate placenta praevia or other serious complications^[7].

Causes and risk factors

The exact cause of placenta praevia is unknown. However, researchers have identified a connection between damage to the lining of the uterus (endometrium) and uterine scarring^[4][7]. When a fertilized egg implants in the uterus, it requires an environment rich in oxygen and collagen. Previous uterine scars may provide this type of environment in the lower part of the uterus, potentially leading to low implantation^[4].

Several factors increase the risk of developing placenta praevia^[1][4][5]:

• Previous cesarean section (C-section) delivery or other uterine surgery, such as removal of fibroids or dilation and curettage (D&C, a procedure sometimes performed after miscarriage)
• Maternal age of 35 years or older
• Having been pregnant multiple times before (multiparity)
• Smoking cigarettes or using cocaine during pregnancy
• Carrying twins, triplets, or more (multiple pregnancy)
• Previous history of placenta praevia in an earlier pregnancy
• History of uterine fibroids (noncancerous growths in the uterus)
• Use of assisted reproductive technology (such as in vitro fertilization or IVF)
• Becoming pregnant again shortly after a previous pregnancy

Among these risk factors, previous uterine scars from cesarean sections or D&C procedures are the most significant, accounting for a large percentage of placenta praevia cases^[4].

How is it diagnosed?

Placenta praevia is typically diagnosed through ultrasound examination^[1][9]. Most cases are identified during routine prenatal ultrasound appointments in the second trimester, often around 18 to 20 weeks of pregnancy. Some cases are discovered after a woman experiences vaginal bleeding and seeks medical attention^[4].

The diagnostic process usually involves^[9]:

• Abdominal ultrasound: An ultrasound device is used on the abdomen to create images of the uterus and placenta
• Transvaginal ultrasound: For more detailed and accurate images, a wand-like device may be placed inside the vagina. Healthcare providers take care with the positioning to avoid disturbing the placenta or causing bleeding
• Some cases may require additional imaging with magnetic resonance imaging (MRI) for clearer visualization

Once placenta praevia is diagnosed, women typically have more frequent ultrasound examinations throughout pregnancy to monitor any changes in the placenta’s position^[9]. It is very important that women diagnosed with placenta praevia inform all healthcare providers about their condition, as digital vaginal examinations (internal examinations of the cervix) must be strictly avoided to prevent triggering severe bleeding^[7][18].

Possible complications

Placenta praevia can lead to serious complications for both mother and baby^[4][7]:

Maternal complications include:

• Major bleeding (hemorrhage) before, during, or after delivery, which may require blood transfusions
• Shock from severe blood loss
• Emergency cesarean delivery
• Increased risk of placenta accreta spectrum disorders, where the placenta attaches too deeply to the uterine wall and may not detach properly after delivery
• Possible need for hysterectomy (surgical removal of the uterus) if bleeding cannot be controlled, resulting in infertility
• Admission to intensive care unit
• In rare cases, death

Complications for the baby include^[7]:

• Premature birth (delivery before 37 weeks), which may be necessary to protect the mother’s health
• Low birth weight
• Breathing problems and other issues related to prematurity
• Lack of oxygen (fetal distress) if severe bleeding occurs
• Need for admission to neonatal intensive care unit
• Increased risk of death

Placenta praevia is also associated with slowed growth of the baby in the uterus and may affect the baby’s ability to move into the correct position for delivery^[13]. More than half of babies in pregnancies with placenta praevia experience some adverse outcomes^[4].

Treatment and management

There is no treatment to change the position of the placenta in the uterus^[7][17]. The goal of managing placenta praevia is to ease symptoms and prolong the pregnancy safely until the baby’s lungs are developed enough for delivery, usually until at least 36 weeks^[1][9].

Treatment varies depending on several factors, including the amount of bleeding, the gestational age of the baby, the baby’s position in the uterus, and the overall health of both mother and baby^[4][9].

If bleeding is minimal or absent:

• Regular monitoring with frequent ultrasounds and prenatal visits
• Reducing activities or modified bed rest
• Pelvic rest, which means no sexual intercourse, no tampons, and no douching. Nothing should be placed in the vagina^[1][17]
• Having a telephone nearby at all times in case emergency help is needed^[18]
• Avoiding strenuous activities or, in severe cases, complete bed rest

If bleeding occurs before 36 weeks^[9]:

• Hospitalization is usually required so the healthcare team can closely monitor both mother and baby
• Monitoring of the baby’s heart rate
• If bleeding stops, women may be able to go home but must be ready to return to the hospital quickly if bleeding resumes
• Blood transfusions may be necessary if blood loss is severe
• Medications to prevent early labor
• Medicines to help the baby’s lungs mature faster in case early delivery is necessary
• If the mother’s blood type is Rh-negative, a special injection called Rhogam may be given^[1]
• Emergency C-section may be performed if bleeding is heavy and cannot be controlled, or if the baby’s heart rate becomes abnormal

Healthcare providers may take a sample of the fluid around the baby (amniotic fluid) to test whether the baby’s lungs have developed enough for early delivery if necessary^[8].

Delivery options

Nearly all women with placenta praevia require delivery by cesarean section (C-section)^[1][3]. If the placenta covers all or part of the cervix, attempting vaginal delivery would cause severe, life-threatening bleeding for both mother and baby^[1][4].

Doctors typically try to schedule the C-section before labor begins, as going into labor may trigger bleeding. If doctors determine that the baby’s lungs are developed enough (usually after 36 weeks of pregnancy), they will perform the C-section^[8][9].

In some cases of marginal placenta praevia, where the placenta is near but not covering the cervix, vaginal delivery might be possible. However, this decision should be made carefully in consultation with the healthcare team^[13].

Women who have placenta praevia should prepare for the possibility of early delivery by^[16]:

• Discussing the delivery plan with their healthcare provider
• Packing a hospital bag ahead of time
• Arranging for help at home during recovery
• Understanding that a C-section may be necessary

Living with placenta praevia

Living with placenta praevia can be emotionally and physically challenging. Women should take several precautions to ensure the best possible outcome^[16][17][18]:

Do:

• Follow your healthcare provider’s guidelines closely
• Watch for any vaginal bleeding or signs of labor and report them immediately
• Attend all scheduled appointments and ultrasounds
• Rest as recommended by your healthcare team
• Keep track of your baby’s movements as instructed by your provider
• Have support readily available at all times
• Take any prescribed medications as directed
• Build a strong support system including your partner, family, friends, and healthcare providers
• Consider joining a support group for women with high-risk pregnancies

Don’t:

• Ignore any symptoms like cramping or bleeding, even if minor
• Have sexual intercourse after 28 weeks of pregnancy (or as advised by your provider)^[18]
• Use tampons or douches, or put anything into the vagina
• Participate in strenuous activities unless approved by your healthcare provider
• Use tobacco, cannabis, or other substances, as they can harm your health and your baby’s development^[18]
• Drink alcohol during pregnancy

Pregnancy with complications like placenta praevia can cause increased stress and anxiety. It is important to talk with your healthcare provider about how you are feeling emotionally and any concerns you may have^[18]. Don’t hesitate to ask for help with daily tasks or emotional support when needed^[16].

Outlook

The outlook for women with placenta praevia has improved significantly with modern prenatal care and monitoring. Many cases diagnosed early in pregnancy resolve on their own as the uterus grows and the placenta moves upward, away from the cervix^[5][13].

For women who continue to have placenta praevia at the time of delivery, careful management and planned cesarean delivery can help ensure the safety of both mother and baby. Regular prenatal care is essential for diagnosing the condition before symptoms appear, allowing the healthcare team and mother to take steps to minimize risks^[1].

Women who have had placenta praevia in one pregnancy have a 2 to 3 in 100 (2 to 3 percent) chance of having it again in future pregnancies^[5]. To minimize the risk of placenta praevia in future pregnancies, healthcare providers recommend having a cesarean section only when medically necessary^[17].

If you experience vaginal bleeding during pregnancy, seek medical attention immediately. Call emergency services if you experience severe or continuous bleeding, pass out, feel dizzy or light-headed, have sharp or severe pain in your belly or pelvis, or notice your baby has stopped moving^[18].