When a pregnant person’s placenta covers the opening of the uterus (the cervix), the condition is known as placenta previa. In most cases, a person with placenta previa cannot safely deliver the baby vaginally; instead, a Cesarean section (or C-section) will need to be performed to deliver the infant safely. What’s more, placenta previa is a risk factor for severe bleeding before, during and after delivery, which can lead to complications and, in extremely rare cases in the U.S., death of the mother and baby.

Placenta previa is often diagnosed at the anatomy ultrasound, during the early part pregnancy. Sometimes individuals may experience painless vaginal bleeding in the second or third trimester of their pregnancy, which leads to the diagnosis of placenta previa.

It’s estimated that as many as 1 in 200 pregnant individuals have a diagnosis of placenta previa at some point during pregnancy. However, in 90% of cases, during the course of the pregnancy, placenta previa resolves on its own—the placenta stops covering the cervix as the uterus grows. As a result, it’s estimated that only 1 in 800 pregnant individuals continue to have the diagnosis of placenta previa at delivery.

When the placenta isn’t in an ideal location, for instance, the baby may be unable to move into the correct position within the pelvis for delivery. Sometimes, placenta previa can impact the baby’s growth in utero. In other cases, the condition can cause the membranes to rupture prematurely and may lead to premature birth.

There are no treatments for placenta previa. If placenta previa persists until the time of delivery then a C-section is often the best and safest route of delivery.

Placenta previa occurs when the placenta—the organ that provides nutrients to a growing fetus—becomes attached to the lowest part of the uterus, covering part or all of the cervix. This condition makes attempts at vaginal childbirth dangerous for the pregnant person and baby.

During pregnancy, the placenta attaches to the inner wall of the mother’s uterus. An umbilical cord runs from the placenta to the fetus’s navel region, delivering nutrition and oxygen to the fetus throughout the pregnancy.

Once the placenta attaches to the uterine wall, it remains in place throughout the pregnancy. As the fetus grows and the uterus becomes larger, the location of the placenta may change, even though it remains attached to the uterine wall.

In most pregnancies, the placenta attaches to a middle or higher section of the uterine wall. As the uterus expands during the pregnancy, the placenta shifts to a higher location in the uterus.

When a person has placenta previa, however, the placenta attaches to a lower section of the uterine wall and it may partly or completely cover the cervix. The placenta can still move as the uterus expands but it may never move from covering the cervix completely.

There are two types of placenta previa:

• Marginal placenta previa, or a low-lying placenta that is near the cervix (within 2 centimeters) but doesn’t cover it
• Placenta previa, when the placenta covers a portion or all of the cervical opening

When a person has a placenta previa, the baby must be delivered via C-section. Attempting to deliver the baby vaginally is too risky, even if the entire cervix isn’t covered with the placenta. Vaginal delivery would cause the placenta to detach from the uterine wall, limiting the baby’s supply of blood and oxygen through the umbilical cord and cause bleeding in the pregnant person. Individuals with a marginal placenta previa may be able to deliver vaginally but this conversation should be had with a doctor or high-risk pregnancy specialist.

Doctors don’t yet know what causes placenta previa. However, the condition is more likely to arise in individuals who:

• Are 35 or older
• Have had infertility treatments
• Were previously pregnant
• Became pregnant again after a short time
• Are having twins, triplets, or other multiples
• Had one or more previous C-sections
• Were diagnosed with and/or had surgery to remove fibroids
• Have had other surgical procedures on the uterus, such as dilation and curettages
• Are smokers
• Use cocaine

Placenta previa typically does not cause any symptoms for the pregnant individual. The primary symptom, if one does occur, is bleeding during the second trimester of pregnancy or later. The blood is typically bright red, and the bleeding, though painless, may be heavy. In some individuals, bleeding may be accompanied by uterine contractions, an increased heart rate, and/or low blood pressure. In rare cases, an individual may experience bleeding so severe that they go into shock from the blood loss, putting both the pregnant individual and baby at risk for death.

Doctors typically diagnose placenta previa early in a pregnancy via ultrasound. However, it can also be diagnosed if an individual experiences bleeding during pregnancy.

Ultrasound is the key diagnostic test used to confirm placenta previa. This helps doctors determine the location of the placenta.

Doctors consider several factors, including the amount of bleeding that has occurred and gestational age, before making a management plan for patients with placenta previa and bleeding. If a C-section delivery is necessary, it may be delayed for weeks or months after a bleeding episode with a placental previa to allow a fetus to mature and avoid premature birth. Individuals with a placenta previa that do not experience bleeding can expect to deliver at full term.

Management options for pregnant individuals with placenta previa can include:

• Avoidance of vaginal intercourse for the remainder of pregnancy
• Hospitalization, to monitor a pregnant person and the fetus for part of or the remainder of pregnancy if bleeding recurs
• Emergency C-section delivery, if a premature fetus is in distress; doctors may give corticosteroid injections to help the baby’s lungs mature before delivery if the pregnancy has not reached 34 weeks
• C-section delivery at 37 weeks’ pregnancy, if the fetus is not in distress
• Blood transfusions, as needed, if the pregnant individual loses a significant amount of blood

In the majority of cases, a person with placenta previa can safely deliver via C-section with no complications.

The condition comes with a risk of increased bleeding, which can be life-threatening for the pregnant individual and/or baby. When appropriate, doctors may hospitalize pregnant people to minimize complications. In some cases, if doctors are unable to stop the bleeding caused by placenta previa after C-section, an emergency hysterectomy may be necessary. This stops the bleeding but prevents a person from becoming pregnant again.

“The setup of Yale New Haven Hospital makes it a safe and place for individuals with placenta previa to deliver,” says Audrey Merriam, MD, MS, a high-risk pregnancy specialist at Yale Medicine. “We have high-risk pregnancy doctors in the hospital 24/7 to assist in the care of these individuals. Additionally, we have the presence of obstetric anesthesiologists that receive extra training in the care of pregnant individuals and the specifics of how to treat potential hemorrhages, since it is different than in the general population. We also have other specialists, such as interventional radiologists, in the hospital which offer other treatment options and use of a hysterectomy as a solution to complicated bleeding situations that may arise with placenta previa. Finally, if you have bleeding with a placenta previa and need to be hospitalized, our Maternal Special Care Unit is recently renovated with all private rooms to make your stay as comfortable as possible.”