The placenta is the organ that anchors a fetus in its mother's womb and works as a conduit, drawing in nutrition and pushing out waste. In a normal pregnancy, the placenta is located at the top or side of the mother's uterus. With placenta previa, however, this temporary organ develops lower in the uterus, covering the cervical opening and causing bleeding during pregnancy as well as during and after birth.
In many cases, the condition is self-correcting as the pregnancy progresses. However, there are situations where the placenta continues to block the cervical opening even as the mother goes into labor. In these cases, a cesarean section is needed to ensure a safe delivery.
Placenta previa symptoms
There are two types of placenta previa: symptomatic and asymptomatic. In most cases, placenta previa is asymptomatic. Many gynecologists encounter the condition only after the patient is already well into labor in a delivery suite, stated Cristina Perez, M.D., an OB-GYN in Houston.
For symptomatic placenta previa, painless vaginal bleeding starting at about 32 weeks of pregnancy is the most common presentation. After that, the bleeding usually stops without any treatment. Bleeding may be triggered by sexual contact or even a routine medical exam. In some cases, the bleeding may be accompanied by uterine pain similar to the contractions experienced during labor.
"In my experience, about 50 percent of pregnant women have placenta previa at 20 weeks but are unaware of it," said Alan Lindemann, M.D., an OB-GYN and maternal mortality expert based in North Dakota.
Many gynecologists encounter the condition only after the patient is already well into labor in a delivery suite.
Talking about placenta previa can be tough for patients, Lindemann explained.
"Placenta previa is so common and so asymptomatic that I had a hard time talking with my patients about it because it scares them," he said. "I know 99 percent of the time, the placenta previa will resolve on its own."
Even though most cases resolve on their own, any bleeding experienced during the second or third trimester of pregnancy should be considered an emergency that calls for immediate medical attention.
"By the third trimester, about 1 in 200 pregnant women will have placenta previa. This is a very small number, but very real if you are the one in 200," Lindemann said.
Who is at risk of placenta previa?
Not all women experience placenta previa during pregnancy. However, research suggests some women have a higher risk than others of developing the condition.
A 2022 umbrella review published in the medical journal Placenta indicated strong evidence for the following risk factors of placenta previa:
- Maternal age, specifically, mothers older than age 35
- A male fetus
- A previous C-section
- A prior abortion
- Pregnancies through assisted reproductive technology (ART) or pharmaceutical solutions for infertility
- A history of smoking
The review also identified weak evidence of a higher risk for placenta previa associated with maternal cocaine use and endometriosis.
However, there is no known primary cause of placenta previa, Perez advised, and patients may not even know they have it until they start to bleed.
Placenta previa is not usually life-threatening but can lead to significant complications, such as a C-section delivery if there is no time for labor to start naturally, Perez explained.
If not caught in time and monitored closely throughout pregnancy, the condition may lead to the following complications:
- Potentially life-threatening bleeding (hemorrhaging) during pregnancy, as well as severe hemorrhaging during labor, delivery and in the first two hours following childbirth.
- Premature birth prompted by bleeding, usually through an emergency cesarean section.
- Stillbirth in extreme cases.
- A secondary condition called placenta accreta spectrum, where the placenta roots itself well beyond the wall of the uterus and increases the risk of extreme bleeding.
Placenta previa treatment
The treatment for this condition depends on how soon a gynecologist can make a diagnosis. In asymptomatic placenta previa, the condition is detected with an ultrasound.
However, since there is no way to get the placenta to move, there is no medical intervention, Lindemann explained. If your placenta previa persists into the third trimester, you may have to deliver via C-section before your baby is full term.
Treatment may consist of the following:
- Vaginal rest, meaning no activities that may trigger bleeding. These actions include sexual intercourse or any sexual activity that leads to an orgasm, exercise in any form, any form of lifting, and even standing for an extended amount of time.
- Vigilance and immediate medical care in the event of bleeding.
- Bed rest may be recommended, but hospital confinement is usually not necessary.
Any expectant mother who experiences bleeding 20 weeks into her pregnancy must call her doctor right away. In the case of heavy bleeding, seek immediate medical treatment.