Placenta Previa: Definition, Symptoms & Risks

Instructor: Sarah Lawson

Sarah has taught nursing courses and has a master's degree in nursing education.

Many potential complications can occur during pregnancy. One complication that can arise is placenta previa. Learn more about placenta previa and its associated symptoms and risks in this lesson.

What is Placenta Previa?

Pregnancy is a very complex process. As with any complex process, there are many problems that can arise. Placenta previa is just one of these potential problems. It occurs when the placenta partially or totally covers the cervix. The cervix is located at the lower end of the uterus and is the opening into the vagina or birth canal. Babies have to pass through the cervix to be born through the vagina. Placenta previa is a big problem because it causes the placenta to partially or totally block the baby's exit.

So what is this placenta that can cause so much trouble? It turns out it's very important -- the placenta is responsible for keeping the baby alive while in utero. It provides oxygen and nutrients to the growing baby and also removes waste from baby's blood. In most pregnancies, the placenta attaches at the top or side of the uterine wall. In placenta previa, the placenta attaches lower in the uterus.

Female reproductive system
Female reproductive system

Placenta previa occurs in approximately 1 in every 200 pregnancies. There are three different types of placenta previa:

  • Complete previa: cervical opening is completely covered by the placenta
  • Partial previa: cervical opening is partially covered by the placenta
  • Marginal previa: placenta extends just to the edge of the cervix

Normal placenta on left; Placenta previa on right

Symptoms

The main symptom of placenta previa is bright red, painless vaginal bleeding. This bleeding usually occurs in the second or third trimester and is usually the first sign of placenta previa. The bleeding may range from light to heavy. It often will resolve without treatment but will almost always return in the days or weeks following.

Some women will also experience premature contractions. Other symptoms that may indicate placenta previa include breech or transverse presentation of the baby and a uterus that measures large for gestational age.

Risks

The placenta will grow wherever the embryo implants in the uterus. If the embryo implants in the lower portion of the uterus, it is possible the placenta may grow over the cervix and cause a placenta previa.

Placenta previa is usually diagnosed during a second trimester ultrasound. It is possible, with a marginal previa, that expansion of the uterus as the baby grows will cause the placenta to move away from the cervix and resolve the situation. If the previa is complete or partial, it is unlikely it will move enough as the uterus expands. The later in a pregnancy that a placenta previa exists, the more likely it is that it will remain at the time of delivery.

Risk factors for having a placenta previa are:

  • Having scars in the lining of the uterus from previous surgery or cesarean sections (C-sections)
  • Having a large placenta, such as having a multiple pregnancy
  • Being of advanced maternal age (35 or older during pregnancy)
  • Having had previous pregnancies, especially if placenta previa occurred during them
  • Being non-Caucasian (race other than white)
  • Smoking cigarettes or using cocaine

To unlock this lesson you must be a Study.com Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use Study.com

Become a Study.com member and start learning now.
Become a Member  Back
What teachers are saying about Study.com
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? Study.com has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account
Support