What is Placenta Previa?

Watch Out for Painless Vaginal Bleeding in Your Third Trimester

There are three types of placenta previa.
There are three types of placenta previa. Wolters Kluwer Health, Inc.- Lippincott Williams & Wilkins. All rights reserved.

During pregnancy, the placenta normally attaches to the upper part of the uterus, away from the cervix. With placenta previa, the placenta attaches low within the uterus, covering all or part of the cervix.

This can be problematic later on in pregnancy, as it may cause severe bleeding, leading to a preterm delivery.

What are the Three Types of Placenta Previa? 

  • Complete previa: the cervical opening (where the cervix opens into the uterus) is completely covered by the placenta
  • Partial previa: some of the cervical opening is covered by the placenta
  • Marginal previa: the placenta extends to edge of the cevix (so close by but not covering)

How is Placenta Previa Diagnosed?

During a second trimester ultrasound, (done in many places on a routine basis around the 20th week) some women will get a diagnosis of placenta previa. The good news is that the majority of these placenta previas resolve on their own. 

Other women may receive a diagnosis of placenta previa when they begin experiencing painless bleeding from their vagina during the third trimester. That being said, it's important to note that not all women with placenta previa experience bleeding. In addition to vaginal bleeding, some women also experience premature uterine contractions. 

Risks of Placenta Previa for Mother and Baby

True placenta previa at full term is serious. Some potential complications for the baby include:

  • health problems for the baby, requiring a NICU admission
  • preterm birth 
  • intrauterine growth restriction (IUGR) due to poor placental perfusion
  • increased risk of perinatal/neonatal death (stillbirth or babies who die within one week to one month of life).

This increased risk of perinatal or neonatal death is a result of babies being born early.

For mothers in advanced countries like the United States, placenta previa is rarely fatal. That being said, bleeding may occur prior to, during, or after labor and delivery. Sometimes, a woman may require blood transfusions for severe, life-threatening bleeding. 

Other potential risks for a mother from having placenta previa include:

  • preterm labor and premature rupture of membranes
  • need for a cesarean delivery (this is common)
  • increased risk of placenta accreta (this is when the placenta attaches directly to the uterine muscle)

Treatment for Placenta Previa in the Third Trimester

If you have persistent placenta previa in the third trimester, your doctor may advise that you avoid sex, strenuous exercise, and using tampons. A doctor may also recommend bed rest, frequently in the hospital. Depending on the gestational age, steroid shots may be given to help mature the baby's lungs.

If the placenta previa does not resolve by the third trimester, a cesarean delivery will nearly always be performed. In addition, if at anytime, the bleeding cannot be controlled, an immediate cesarean delivery is needed. 

Am I At Risk for Placenta Previa?

There are a number of potential factors that may increase a woman's chance of having a placenta previa.

Remember, your chance of having a placenta previa is still low (about one in two hundred women in the third trimester), even if you have one or more of these risk factors:

  • previous placenta previa
  • advanced maternal age
  • increased parity (number of pregnancies)
  • being pregnant with more than one baby (for example, twins or triplets)
  • previous uterine surgery, including cesarean section (regardless of incision type) or a D&C
  • prior abortion
  • infertility treatment
  • smoke cigarettes
  • cocaine use 

A Word From Verywell

Placenta previa can be a stressful diagnosis for all involved. The period of time from the diagnosis to the delivery are often periods of great worry and fear.

The good news is that there are support groups for those who have been diagnosed with placenta previa, and/or who are under bed rest orders.

Be sure to reach out to your doctor if you experience any vaginal bleeding during pregnancy, or if you have any questions or concerns related to your placenta previa or pregnancy in general. 

Sources:

American Pregnancy Association. (2015). Placenta Previa.

Lockwood CJ, Russo-Stieglitz K. Clinical features, diagnosis, and course of placenta previa. In: UpToDate, Levine D, Ramin SM (Eds), UpToDate, Waltham, MA. 

March of Dimes. (2012). Placenta Previa. 

Sakornbut E, Leeman L, Fontaine P. Late pregnancy bleeding. Am Fam Physician. 2007 Apr 15;75(8):1199-1206.

Vahanian SA, Lavery JA, Ananth CV, Vintzileos A. Placental implantation abnormalities and risk of preterm delivery: a systematic review and metaanalysis. Am J Obstet Gynecol. 2015 Oct;213(4 Suppl):S78-90.

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