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Placenta Previa

  • Author: Ronan Bakker, MD; Chief Editor: Carl V Smith, MD  more...
 
Updated: May 12, 2016
 

Background

Placenta previa is an obstetric complication that classically presents as painless vaginal bleeding in the third trimester secondary to an abnormal placentation near or covering the internal cervical os. However, with the technologic advances in ultrasonography, the diagnosis of placenta previa is commonly made earlier in pregnancy. Historically, there have been three defined types of placenta previa: complete, partial, and marginal. More recently, these definitions have been consolidated into two definitions: complete and marginal previa.

A complete previa is defined as complete coverage of the cervical os by the placenta. If the leading edge of the placenta is less than 2 cm from the internal os, but not fully covering, it is considered a marginal previa (see the following image). Because of the inherent risk of hemorrhage, placenta previa may cause serious morbidity and mortality to both the fetus and the mother.

Placenta previa. Placenta previa.
Complete placenta previa noted on ultrasound. Complete placenta previa noted on ultrasound.
 Another ultrasound image clearly depicting comple Another ultrasound image clearly depicting complete placenta previa.
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Pathophysiology

Placental implantation is initiated by the embryo (embryonic plate) adhering in the lower (caudad) uterus. With placental attachment and growth, the developing placenta may cover the cervical os. However, it is thought that a defective decidual vascularization occurs over the cervix, possibly secondary to inflammatory or atrophic changes. As such, sections of the placenta having undergone atrophic changes could persist as a vasa previa.

A leading cause of third-trimester hemorrhage, placenta previa presents classically as painless bleeding. Bleeding is thought to occur in association with the development of the lower uterine segment in the third trimester. Placental attachment is disrupted as this area gradually thins in preparation for the onset of labor; this leads to bleeding at the implantation site, because the uterus is unable to contract adequately and stop the flow of blood from the open vessels. Thrombin release from the bleeding sites promotes uterine contractions and leads to a vicious cycle of bleeding–contractions–placental separation–bleeding.

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Etiology

The exact etiology of placenta previa is unknown. The condition may be multifactorial and is postulated to be related to the following risk factors:

  • Advancing maternal age (>35 y)
  • Infertility treatment
  • Multiparity (5% in grand multiparous patients)
  • Multiple gestation
  • Short interpregnancy interval
  • Previous uterine surgery, uterine insult or injury
  • Previous cesarean delivery, [1, 2] including first subsequent pregnancy following a cesarean delivery [1]
  • Previous or recurrent abortions
  • Previous placenta previa (4-8%)
  • Nonwhite ethnicity
  • Low socioeconomic status
  • Smoking
  • Cocaine use

Unlike first-trimester bleeding, second- and third-trimester bleeding is usually due to abnormal placental implantation.

Hemorrhaging, if associated with labor, would be secondary to cervical dilatation and disruption of the placental implantation from the cervix and lower uterine segment. As noted previously, the lower uterine segment is inefficient in contracting and thus cannot constrict vessels as in the uterine corpus, resulting in continued bleeding (see Pathophysiology).

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Epidemiology

United States statistics

Placenta previa is frequently reported to occur in 0.5% of all US pregnancies. A large, US population-based, 1989-1997 study indicated an incidence of 2.8 per 1000 live births.[3] The risks increase 1.5- to 5-fold with a history of cesarean delivery. A meta-analysis showed that the rate of placenta previa increases with increasing numbers of cesarean deliveries, with a rate of 1% after 1 cesarean delivery, 2.8% after 3 cesarean deliveries, and as high as 3.7% after 5 cesarean deliveries.[1]

Racial and age-related differences in incidence

The significance of race in having a role in placenta previa is somewhat controversial. Some studies suggest an increased risk among black and Asian women, whereas other studies cite no difference.[4]

Advanced maternal age has also been strongly associated with an increasing incidence of placenta previa. The incidence of placenta previa after age 35 years reported to be 2%. A further increase to 5% is seen after age 40 years, which is a 9-fold increase when compared to females younger than 20 years.[5, 6]

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Prognosis

Placenta previa complicates approximately 0.5% of all pregnancies.[4] Technologic advances in ultrasonography have increased the early diagnosis of placenta previa, and several studies have shown that a significant portion of these early diagnoses do not persist until delivery.[7, 8] In fact, 90% of all placentas designated as “low lying” on an early sonogram are no longer present on repeat examination in the third trimester.[9]

However, maternal and fetal complications of placenta previa are well documented. Preterm birth is highly associated with placenta previa, with 16.9% of women delivering at less than 34 weeks and 27.5% delivering between 34 and 37 weeks in a population-based study from 1989 to 1997.[3] There is a significant increase in the risk of postpartum hemorrhage and need for emergency hysterectomy in women with placenta previa.[10]

Maternal complications of placenta previa are summarized as follows:

  • Hemorrhage, [11] including rebleeding (Planning delivery and control of hemorrhage is critical in cases of placenta previa as well as placenta accreta, increta, and percreta.)
  • Higher rates of blood transfusion [11, 12]
  • Placental abruption
  • Preterm delivery
  • Increased incidence of postpartum endometritis [12]
  • Mortality rate (2-3%); in the US, the maternal mortality rate is 0.03%, the great majority of which is related to uterine bleeding and the complication of disseminated intravascular coagulopathy

The Table, below, summarizes the relative risk of some morbidities in women with placenta previa.

Table. Relative Risk of Morbidities in Patients With Placenta Previa (Open Table in a new window)

Morbidities Relative Risk
Antepartum bleeding 10
Need for hysterectomy 33
Blood transfusion 10
Septicemia 5.5
Thrombophlebitis 5
Endometritis 6.6[12]

 

Complications of placenta previa in the neonate/infant are summarized as follows:

  • Congenital malformations
  • Fetal intrauterine growth retardation (IUGR)
  • Fetal anemia and Rh isoimmunization
  • Abnormal fetal presentation
  • Low birth weight (< 2500 g) [12]
  • Neonatal respiratory distress syndrome [12]
  • Jaundice [12]
  • Admission to the neonatal intensive care unit (NICU) [12]
  • Longer hospital stay [12]
  • Increased risk for infant neurodevelopmental delay and sudden infant death syndrome (SIDS) [13]
  • Neonatal mortality rate: As high as 1.2% in the United States [14]
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Patient Education

Patients with placenta previa should decrease activity to avoid rebleeding. In addition, pelvic examinations and intercourse should be avoided.

Counsel patients with placenta previa about the risk of recurrence. Instruct them to notify the obstetrician caring for their next pregnancy about their history of placenta previa.

Encourage patients with known placenta previa to maintain intake of iron and folate as a safety margin in the event of bleeding.

For patient education resources, see Pregnancy Center and Women's Health Center, as well as Bleeding During Pregnancy, and Vaginal Bleeding.

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Contributor Information and Disclosures
Author

Ronan Bakker, MD Resident Physician, Department of Obstetrics and Gynecology, Virginia Commonwealth University Health System

Ronan Bakker, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Medical Association

Disclosure: Nothing to disclose.

Coauthor(s)

Ronald M Ramus, MD Professor of Obstetrics and Gynecology, Director, Division of Maternal-Fetal Medicine, Virginia Commonwealth University School of Medicine

Ronald M Ramus, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, Medical Society of Virginia, Society for Maternal-Fetal Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

John G Pierce, Jr, MD Associate Professor, Departments of Obstetrics/Gynecology and Internal Medicine, Medical College of Virginia at Virginia Commonwealth University

John G Pierce, Jr, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, Association of Professors of Gynecology and Obstetrics, Christian Medical and Dental Associations, Medical Society of Virginia, Society of Laparoendoscopic Surgeons

Disclosure: Nothing to disclose.

Chief Editor

Carl V Smith, MD The Distinguished Chris J and Marie A Olson Chair of Obstetrics and Gynecology, Professor, Department of Obstetrics and Gynecology, Senior Associate Dean for Clinical Affairs, University of Nebraska Medical Center

Carl V Smith, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, Association of Professors of Gynecology and Obstetrics, Central Association of Obstetricians and Gynecologists, Society for Maternal-Fetal Medicine, Council of University Chairs of Obstetrics and Gynecology, Nebraska Medical Association

Disclosure: Nothing to disclose.

Additional Contributors

Saju Joy, MD, MS Associate Director, Division Chief of Maternal-Fetal Medicine, Department of Obstetrics and Gynecology, Carolinas Medical Center

Saju Joy, MD, MS is a member of the following medical societies: American College of Obstetricians and Gynecologists, American Institute of Ultrasound in Medicine, Society for Maternal-Fetal Medicine, American Medical Association

Disclosure: Nothing to disclose.

Matthew M Finneran, MD Resident Physician, Department of Obstetrics and Gynecology, Carolinas Healthcare System

Disclosure: Nothing to disclose.

Acknowledgements

Pamela L Dyne, MD Professor of Clinical Medicine/Emergency Medicine, University of California, Los Angeles, David Geffen School of Medicine; Attending Physician, Department of Emergency Medicine, Olive View-UCLA Medical Center

Pamela L Dyne, MD is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Patrick Ko, MD Clinical Assistant Professor, Department of Emergency Medicine, New York University Medical School; Assistant Program Director, Department of Emergency Medicine, North Shore University Hospital

Patrick Ko, MD is a member of the following medical societies: American College of Emergency Physicians and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Deborah Lyon, MD Director, Division of Gynecology, Associate Professor, Department of Obstetrics and Gynecology, University of Florida Health Science Center at Jacksonville

Deborah Lyon, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, Association of American Medical Colleges, Association of Professors of Gynecology and Obstetrics, and Florida Medical Association

Disclosure: Nothing to disclose.

John G Pierce Jr, MD Associate Professor, Departments of Obstetrics/Gynecology and Internal Medicine, Medical College of Virginia at Virginia Commonwealth University

John G Pierce Jr, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists, Association of Professors of Gynecology and Obstetrics, Christian Medical & Dental Society, Medical Society of Virginia, and Society of Laparoendoscopic Surgeons

Disclosure: Nothing to disclose.

Joseph J Sachter, MD, FACEP Consulting Staff, Department of Emergency Medicine, Muhlenberg Regional Medical Center

Joseph J Sachter, MD, FACEP is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, American College of Physician Executives, American Medical Association, and Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Ryan A Stone, MD Fellow, Department of Obstetrics and Gynecology, Maternal-Fetal Medicine Section, Wake Forest University Health Sciences

Ryan A Stone, MD is a member of the following medical societies: Academic Pediatric Association, American College of Obstetricians and Gynecologists, American Medical Association, and Society for Maternal-Fetal Medicine

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Salary Employment

Lorene Temming, MD Resident Physician, Department of Obstetrics and Gynecology, Carolinas Medical Center

Lorene Temming, MD is a member of the following medical societies: American College of Obstetricians and Gynecologists and North Carolina Medical Society

Disclosure: Nothing to disclose.

Young Yoon, MD Associate Director, Assistant Professor, Department of Emergency Medicine, Mount Sinai Medical Center

Young Yoon, MD is a member of the following medical societies: Society for Academic Emergency Medicine

Disclosure: Nothing to disclose.

Mark Zwanger, MD, MBA Assistant Professor, Department of Emergency Medicine, Jefferson Medical College of Thomas Jefferson University

Mark Zwanger, MD, MBA is a member of the following medical societies: American Academy of Emergency Medicine, American College of Emergency Physicians, and American Medical Association

Disclosure: Nothing to disclose.

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Placenta previa.
Complete or total placenta previa. The entire cervical os is covered.
Low-lying placenta previa. The placenta partially separated from the lower uterine segment.
Placenta previa invading the lower uterine segment and covering the cervical os.
Complete placenta previa noted on ultrasound.
Another ultrasound image clearly depicting complete placenta previa.
Table. Relative Risk of Morbidities in Patients With Placenta Previa
Morbidities Relative Risk
Antepartum bleeding 10
Need for hysterectomy 33
Blood transfusion 10
Septicemia 5.5
Thrombophlebitis 5
Endometritis 6.6[12]
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