Placenta praevia is a pregnancy complication where the placenta attaches to the lower part of the uterus and covers all or part of the cervix, the opening to the birth canal. This positioning can prevent a safe vaginal birth and may cause bleeding during pregnancy or delivery. While the condition occurs in about 1 in 200 pregnancies, it often resolves on its own as the uterus grows, though careful monitoring and sometimes early delivery are needed to keep both mother and baby safe.

How Common Is Placenta Praevia

Placenta praevia affects approximately 1 in every 200 pregnancies, making it a relatively uncommon but important pregnancy complication that healthcare providers watch for during routine care^[1]. Healthcare providers typically identify this condition during the second trimester of pregnancy through ultrasound examinations. However, the situation isn’t always as concerning as it might initially seem. In many cases diagnosed early in pregnancy, the problem corrects itself naturally as the pregnancy progresses.

What happens is that as the baby grows and the uterus expands, the placenta often moves upward, away from the cervix. This natural shift occurs in about 90% of cases where placenta praevia is diagnosed early^[13]. As a result, while many pregnant women receive an initial diagnosis of this condition, far fewer continue to have it at the time of delivery. Studies suggest that only about 1 in 800 pregnant women still have placenta praevia when it’s time for their baby to be born^[13].

What Causes Placenta Praevia

The exact cause of placenta praevia remains unknown to medical researchers. However, there is a notable connection between the condition and damage to the uterine lining, which is the inner wall of the womb where the placenta normally attaches^[4]. Scientists believe that when a fertilized egg is ready to implant, it seeks out an environment rich in oxygen and collagen. When the upper parts of the uterus have scarring or damage, the developing placenta may attach lower down in the uterus, closer to or over the cervix.

During a normal pregnancy, the placenta typically attaches to the top or side of the uterus, well away from the cervical opening. This positioning allows the baby to exit through the birth canal without the placenta blocking the way. The placenta is a remarkable organ that develops during pregnancy to provide oxygen and nutrients to the growing baby through the umbilical cord. It also removes waste products from the baby’s blood. In placenta praevia, this vital organ simply attaches in the wrong location^[2].

Risk Factors for Developing Placenta Praevia

While anyone can develop placenta praevia, certain factors significantly increase the likelihood of this complication. Understanding these risk factors helps healthcare providers identify which pregnant women need closer monitoring throughout their pregnancy.

Age plays an important role, as women who are 35 years old or older face a higher risk of developing this condition^[1]. The risk also increases substantially with the number of previous pregnancies a woman has had. Women who have had multiple pregnancies, particularly those who have given birth six or more times, face considerably higher odds of developing placenta praevia^[7].

Previous surgeries on the uterus represent one of the most significant risk factors. Women who have had a Caesarean section (also called a C-section), which is a surgical delivery through the abdomen, are at increased risk. The same applies to those who have undergone a D&C (dilation and curettage), a procedure sometimes performed after a miscarriage or for other medical reasons^[4]. These surgical procedures can create scarring on the uterine lining, which may affect where the placenta attaches in subsequent pregnancies.

Women carrying multiple babies, such as twins or triplets, also have a higher chance of developing placenta praevia^[1]. Additionally, those who have experienced placenta praevia in a previous pregnancy face a 2 to 3 in 100 chance of having it occur again^[5].

Lifestyle habits can contribute to the risk as well. Smoking cigarettes or using cocaine during pregnancy increases the likelihood of this complication^[4]. Women who have had fertility treatments, specifically in vitro fertilization (IVF), where an egg is fertilized outside the body and then implanted in the uterus, also face elevated risk^[5]. Other factors include having uterine fibroids, which are non-cancerous growths in the uterus, or a history of having had other uterine surgeries^[1].

Symptoms of Placenta Praevia

The most recognizable symptom of placenta praevia is sudden, painless vaginal bleeding that typically begins after the 20th week of pregnancy^[2]. This bleeding is usually bright red in color and can range from light spotting to heavy bleeding. What makes this symptom particularly distinctive is that it occurs without the cramping or pain that often accompanies other pregnancy complications.

The bleeding happens because as the pregnancy advances, the lower part of the uterus begins to thin out and stretch to accommodate the growing baby. When the placenta is attached to this lower area, as it is in placenta praevia, this natural stretching and thinning process can separate the placenta from the uterine wall, causing bleeding^[7]. The bleeding might stop on its own, only to start again days or weeks later without warning.

In some women, the bleeding may be triggered by specific events. Sexual intercourse can cause bleeding in women with placenta praevia, which is why healthcare providers typically advise avoiding sex after this condition is diagnosed^[8]. A medical examination, particularly a vaginal exam, can also trigger bleeding. For this reason, once placenta praevia is identified, vaginal examinations are generally avoided throughout the remainder of the pregnancy.

Some women with placenta praevia also experience mild cramping or contractions in the abdomen, belly, or back^[1]. However, it’s important to note that some women have no symptoms at all until labor begins or until their healthcare provider identifies the condition during a routine ultrasound. This is why regular prenatal care and ultrasound examinations are so crucial during pregnancy.

Preventing Placenta Praevia

Unfortunately, there is no known way to prevent placenta praevia from occurring since the exact cause of the condition remains unclear. However, understanding the risk factors can help women make informed choices that might reduce their chances of developing this complication in future pregnancies.

One important consideration is avoiding unnecessary Caesarean sections. Since previous C-sections and uterine surgeries significantly increase the risk of placenta praevia, having a C-section only when medically necessary can help reduce the risk in subsequent pregnancies^[17]. When a vaginal delivery is safe for both mother and baby, it may be the better choice for protecting future pregnancies from this complication.

Avoiding tobacco and cocaine use during pregnancy is another crucial step. Both substances not only increase the risk of placenta praevia but also pose numerous other dangers to the developing baby^[4]. Making healthy lifestyle choices before and during pregnancy can contribute to better outcomes overall.

For women who have had placenta praevia in a previous pregnancy, it’s vital to inform healthcare providers early in any subsequent pregnancy. While the condition cannot be prevented, early awareness allows for appropriate monitoring and preparation. Healthcare providers can schedule more frequent ultrasounds to check the placenta’s position and develop a birth plan that keeps both mother and baby safe.

How Placenta Praevia Affects the Body

Understanding what happens in the body during placenta praevia helps explain why this condition is taken so seriously by healthcare providers. Normally, the placenta attaches high up in the uterus and stays firmly in place throughout pregnancy. After the baby is born during a vaginal delivery, the cervix is already open, and the placenta separates naturally from the uterine wall and is delivered as the afterbirth.

In placenta praevia, the placenta covers part or all of the cervical opening. During labor, the cervix must thin out and open to allow the baby to pass through. When the placenta is positioned over or near the cervix, this natural process of the cervix opening would tear the placenta away from the uterine wall^[7]. This tearing can cause severe, life-threatening bleeding for the mother. It also cuts off the baby’s supply of oxygen and nutrients, which come through the umbilical cord connected to the placenta.

There are different types of placenta praevia, and each affects the body differently. In marginal placenta praevia, the placenta sits at the edge of the cervix, touching it but not covering it. This type is more likely to resolve on its own as the uterus grows^[1]. In partial placenta praevia, the placenta covers part of the cervical opening. In complete placenta praevia, the placenta entirely covers the cervix, completely blocking the baby’s exit path. This last type is less likely to correct itself and presents the highest risk.

The bleeding that occurs with placenta praevia can happen at any point in the second half of pregnancy, not just during labor. As the uterus expands and the lower segment stretches, it can cause the placenta to separate slightly from the uterine wall, triggering bleeding. This is why women diagnosed with this condition need to be vigilant about any signs of bleeding and must avoid activities that might trigger it, such as sexual intercourse or strenuous physical activity^[9].

The condition can also increase the risk of other complications. Women with placenta praevia have a higher chance of developing placenta accreta spectrum, a condition where the placenta attaches too deeply into the uterine wall and has difficulty separating after delivery^[4]. This can lead to severe bleeding after birth and may require additional surgical interventions. In severe cases, the bleeding might be so severe that a hysterectomy, the surgical removal of the uterus, becomes necessary to save the mother’s life.

For the baby, placenta praevia can mean premature birth if bleeding becomes severe and requires early delivery. The condition might also affect the baby’s position in the uterus, making it difficult for the baby to move into the proper head-down position for birth. In some cases, the baby’s growth may be affected if the placenta is not functioning optimally due to its position^[13].