What is Placenta Previa?

Photo by Suhyeon Choi on Unsplash

Written by Hannah Simpson, BSN, RN 

Overview

Placenta previa is a problem with the location of the placenta in pregnancy. The placenta is the organ that provides oxygen and nutrition to the developing baby and removes waste during pregnancy. Typically, the placenta is located at the top or the side of the uterus. However, in placenta previa, the placenta covers all or some of the cervix. This is a problem because the cervix is the opening to the birth canal. When the placenta blocks part or all of the cervix, vaginal delivery can cause life-threatening bleeding. 

Types of placenta previa 

Placenta previa can be marginal, partial, or complete. A marginal placenta previa is located at the edge of the cervix. It comes into contact with the cervix, but it does not block it. This type of placenta previa may resolve on its own before the woman’s due date. This is because as the uterus expands, the placenta may shift upwards and no longer interfere with the cervix. A partial placenta previa blocks part of the cervix. A complete placenta previa covers the entire cervical opening. 

Risk factors 

There are certain factors that make a woman more likely to have placenta previa during her pregnancy. These factors include having previous pregnancies, previous c-section, previous placenta previa, maternal age above 35, smoking, and cocaine use (1). 

Symptoms 

The primary symptom of placenta previa is bright red vaginal bleeding. Although it is possible for women to experience cramping, it is more likely that the bleeding will be without pain. The amount of bleeding can vary, but it is possible that enough bleeding can occur that it can become life-threatening. The bleeding is most likely to begin in the second half of pregnancy. It may be sporadic in nature. It may start, stop, and start again after several days (2). 

Health risks for the mother 

Placenta previa poses certain risks to the health of the mother and the baby. The main risks are bleeding and complications of bleeding. The bleeding can occur during pregnancy, or it can occur during labor and delivery. A blood transfusion may be necessary. A woman with placenta previa can bleed enough for it to be life-threatening. Another risk is early delivery. If a woman with placenta previa begins bleeding uncontrollably, she may require early delivery by c-section. Because of the risk of blood loss, there is also a risk of anemia. Anemia means the woman’s blood supply cannot carry enough oxygen to her body (3). This can cause dizziness, shortness of breath, and fatigue. 

Health risks for the baby 

One of the health risks to the baby is premature birth. If the woman requires early delivery due to severe bleeding, the baby may be born too early. This may result in low birth weight and difficulty breathing if the baby’s lungs are not fully developed at the time of delivery (2).

Diagnosis and treatment 

Placenta previa is usually diagnosed in the second trimester by ultrasound. During pregnancy, placenta previa is treated with pelvic rest (1). Pelvic rest means avoiding putting anything into the vagina or performing any activity that would put stress on the pelvic floor muscles. This is recommended because any manipulation of the placenta can lead to severe bleeding (4). This means avoiding sexual intercourse, douching, and tampons. Depending on the position of the placenta, bed rest may also be indicated. If a substantial amount of bleeding occurs, a blood transfusion may be necessary. Placenta previa nearly always requires a c-section delivery (2). This is because of the risk of severe bleeding during vaginal delivery when the placenta is partially or completely covering the cervix. The bleeding can be severe enough to threaten the life of the mother and the baby. A c-section is usually scheduled electively at 36-37 weeks. If a woman with placenta previa starts bleeding severely during pregnancy, she may require an emergency c-section. 

Conclusion

Placenta previa is a condition where the placenta is not in the right place in the uterus. Instead of being at the top or the side of the uterus, it is partially or completely covering the cervix. This means that vaginal delivery can cause severe bleeding and a c-section is likely required. During pregnancy, management involves avoiding activities that can cause bleeding. This is accomplished by pelvic rest and potentially bed rest. Always consult a healthcare provider for concerns regarding the care and treatment of placenta previa. 

References 

1. Placenta previa: MedlinePlus Medical Encyclopedia. Available from: https://medlineplus.gov/ency/article/000900.htm

2. Cleveland Clinic. Placenta Previa: Symptoms, Causes & Treatments. Available from: https://my.clevelandclinic.org/health/diseases/24211-placenta-previa

3. Anemia: MedlinePlus Medical Encyclopedia. Available from: https://medlineplus.gov/anemia.html

4. Anderson-Bagga FM, Sze A. Placenta Previa. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026. Available from: http://www.ncbi.nlm.nih.gov/books/NBK539818

Assessed and Endorsed by the MedReport Medical Review Board