What Is Placenta Previa? Risk, Symptoms, and Treatment

The placenta doesn't always place itself in the uterus perfectly, and that can lead to a potentially dangerous pregnancy complication called placenta previa.

Pregnant women touches stomach at OB-GYN doctor's office

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When you’re pregnant, it’s easy to forget that a placenta is growing right alongside your baby. It plays a crucial role for your little one, acting as a source of nutrition and oxygen through the umbilical cord. Sometimes, however, the organ can develop complications like placenta previa. Keep reading to learn everything you need to know about placenta previa, including what causes it, how to diagnose it, and whether you’ll experience any symptoms. 

What Causes Placenta Previa? 

After an egg is fertilized at the very beginning of pregnancy, an embryo is formed, and the placenta attaches somewhere in the uterus. In some cases, the placenta can attach to the uterine wall in a spot that isn’t ideal. If a placenta completely or partially covers the cervix (the opening to the birth canal), it can create a potentially dangerous situation called placenta previa.

"Placenta previa is caused by the wrong placement of the placenta over the cervix," explains Marra Francis, M.D., an OB-GYN in Woodlands, Texas, and an author of the Mommy MD Guides. The placenta is usually positioned lower in the uterus with this condition. 

How Common Is Placenta Previa? 

The good news is, placenta previa is a relatively rare condition, occuring in about 1 in 200 pregnancies, according to the Cleveland Clinic. There's nothing you can do to prevent it, and you didn’t do anything wrong to cause placenta previa. "[People] don't have any control over where the placenta attaches on the uterus," says Siobhan Kubesh, a certified midwife with OB-GYN North in Austin.

Placenta Previa Risk Factors

While you can’t prevent placenta previa, there are a few circumstances that tend to make it more likely to occur. Here are some placenta previa risk factors, according to Titi Otunla, a certified nurse midwife at Texas Children's Pavilion for Women in Houston.

  • Advanced maternal age (35 or older)
  • Smoking or drug use
  • Second or subsequent pregnancy
  • Pregnancy with assisted reproductive technology like in vitro fertilization (IVF) 
  • A prior C-section delivery 
  • Previous pregnancy with placenta previa (If you had the condition previously, there’s a 2-3% chance of recurrence, according to March of Dimes.) 
  • Carrying multiples
  • Uterine scars from prior procedures 

Types of Placenta Previa

There is three types of placenta previa: complete, partial, and marginal. They describe the location of the placenta in relation to the cervix. Note that the type of placenta previa you have can change throughout the pregnancy.

  • Complete The placenta fully covers the opening of the cervix. This type of placenta previa is least likely to correct itself.
  • Partial: The placenta partially covers the cervical opening; the other part remains uncovered.
  • Marginal: The placenta is near the cervix but not quite blocking it.

Placenta Previa Symptoms

Typically, pregnant people don’t have any other symptoms associated with placenta previa, and it’s not harmful to baby’s growth and development, says Krista Elkins, B.A., R.N., CFRN, NRP, CCP-C.

That said, some people experience painless, bright red vaginal bleeding, especially after the 12th week of gestation, says Dr. Francis.  But it's important to note that you could bleed without having placenta previa. Mild cramping is also possible. 

Possible Complications of Placenta Previa

Placenta previa usually corrects itself before delivery; otherwise it could be a high-risk pregnancy condition. "In approximately 1 out of 200 pregnancies, the placenta previa continues into the third trimester, making labor dangerous,” says Dr. Francis. “Placenta previa is especially dangerous if the previa is complete—meaning completely covering the cervix—or if the large blood vessels cross over. Bleeding from either of these can result in large volumes of blood loss in the mother very quickly," she says.

Excessive bleeding might also lead to preterm birth, which is associated with health complications for babies. Throughout pregnancy, bleeding might be treated with a blood transfusion and/or an extended hospital stay. 

How is Placenta Previa Diagnosed? 

Placenta previa is most often diagnosed by ultrasound, says Elkins. Your doctor will be able to tell the position of your placenta during a routine ultrasound at any point in your pregnancy. 

“If your placenta is resting low in your uterus early on in your pregnancy, you’ll likely have a few extra ultrasounds to monitor the progress. Since many cases of placenta previa self-resolve over the course of your pregnancy, this is often the only type of monitoring or intervention you’ll need for the condition,” says Elkins. 

Treatment for Placenta Previa 

For most parents-to-be, placenta placement becomes a non-issue as the pregnancy progresses. "The majority of placenta previa will resolve on its own," says Dr. Francis. "As the uterus grows, it pulls up the placenta, and the positioning becomes normal by 20 weeks. But after 20 weeks, if a placenta previa is still present, typically pregnant people will have ultrasounds every 2 to 4 weeks to monitor the previa, as some will still resolve later." 

If your placenta doesn't move to a safer spot in your uterus, placenta previa will affect the way your baby comes into the world. "For the small percentage of women where placenta previa isn't resolved, they [often] have pelvic rest, which means no sex and that nothing goes into the vagina—not even digital exams to see how things are going,"says  Dr. Francis. That's to prevent damage to the placenta that could lead to hemorrhaging and put both you and your baby at risk.

As you can imagine, placenta previa also makes vaginal birth a riskier proposition. "You don't want a woman with placenta previa to go into labor, because if the uterus starts to contract, there could be very brisk bleeding that puts both the mom and the baby at risk," says Dr. Francis. 

If a pregnant person has unresolved placenta previa, their baby is typically delivered early by C-section, as they cannot deliver vaginally. The good news is that placenta previa almost always results in a happy, healthy baby and parent!

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