Overview

Placenta previa is a pregnancy complication that occurs when the placenta attaches low in the uterus and partially or completely covers the cervix. This condition affects approximately 1 in 200 pregnancies and can cause serious complications for both mother and baby if not properly managed.

During a normal pregnancy, the placenta attaches to the upper part of the uterine wall, away from the cervix. However, in placenta previa, the placenta's position can block the baby's exit route during delivery. As the pregnancy progresses and the cervix begins to thin and dilate in preparation for labor, the placenta may tear, leading to bleeding during pregnancy.

There are different types of placenta previa, ranging from minor cases where the placenta is close to but not covering the cervix, to complete placenta previa where the entire cervical opening is blocked. The severity and management of the condition depend on the type and the stage of pregnancy when it's diagnosed. With proper medical care and monitoring, most women with placenta previa can have successful pregnancies, though cesarean delivery is often necessary.

Symptoms

The primary symptom of placenta previa is painless vaginal bleeding during the second or third trimester of pregnancy. However, the presentation can vary, and some women may experience no symptoms until labor begins.

Primary Symptoms

  • Spotting or bleeding during pregnancy - The hallmark symptom, typically bright red and painless
  • Sudden onset of bleeding without warning
  • Bleeding that stops on its own but may recur
  • Light spotting to heavy bleeding episodes

Associated Symptoms

  • Pain during pregnancy - Though classically painless, some women experience mild cramping
  • Cramps and spasms - Mild uterine contractions may accompany bleeding
  • Involuntary urination - Due to pressure on the bladder from the low-lying placenta
  • Premature contractions
  • Breech or abnormal fetal position

Warning Signs

Seek immediate medical attention if you experience:

  • Heavy vaginal bleeding (soaking more than one pad per hour)
  • Bleeding accompanied by severe abdominal pain
  • Signs of shock (dizziness, rapid heartbeat, pale skin)
  • Decreased fetal movement
  • Regular contractions before 37 weeks

Causes

The exact cause of placenta previa is not always clear, but it occurs when the fertilized egg implants in the lower part of the uterus rather than the upper portion. Several factors may contribute to this abnormal placental attachment.

Primary Mechanisms

Abnormal Implantation

The placenta develops where the embryo implants in the uterine wall. If implantation occurs low in the uterus, near or over the cervix, placenta previa results. This may be due to:

  • Scarring in the upper uterine wall from previous surgeries
  • Abnormalities in the uterine lining
  • Large placental size requiring more attachment area

Placental Migration

In many cases diagnosed early in pregnancy, the placenta appears to "move" away from the cervix as the uterus grows. This isn't actual movement but rather differential growth of the uterus that changes the placenta's relative position. However, in true placenta previa, this migration doesn't occur sufficiently.

Contributing Factors

  • Uterine scarring: From previous cesarean sections, surgeries, or procedures
  • Multiple gestations: Twins or higher-order multiples increase placental size
  • Maternal age: Risk increases with advancing maternal age
  • Endometrial damage: From infections, procedures, or smoking
  • Previous placenta previa: Recurrence risk in subsequent pregnancies

Risk Factors

Several factors increase the likelihood of developing placenta previa. Understanding these risks helps in early identification and appropriate monitoring.

Major Risk Factors

  • Previous cesarean delivery: Risk increases with each cesarean section (1% after one, up to 5% after four or more)
  • Multiple pregnancies: Having been pregnant multiple times increases risk
  • Multiple gestation: Carrying twins, triplets, or more
  • Advanced maternal age: Women over 35 have higher risk
  • Previous placenta previa: 4-8% recurrence rate

Additional Risk Factors

  • Smoking: Increases risk by 1.5 to 3 times
  • Cocaine use: Significantly elevates risk
  • Previous uterine surgery: Including myomectomy or D&C procedures
  • Endometriosis: May affect placental implantation
  • In vitro fertilization (IVF): Slightly increased risk
  • Male fetus: Slightly higher risk than with female fetus
  • Non-Caucasian ethnicity: Higher prevalence in Asian populations

Diagnosis

Placenta previa is typically diagnosed through routine ultrasound examinations during pregnancy. Early detection and accurate classification are crucial for appropriate management.

Diagnostic Methods

Transabdominal Ultrasound

The initial screening method during routine prenatal care. Can identify placental location but may be less accurate for diagnosing minor degrees of previa.

Transvaginal Ultrasound

The gold standard for diagnosing placenta previa. Provides more accurate visualization of the relationship between the placental edge and the cervical opening. Despite initial concerns, transvaginal ultrasound is safe in placenta previa when performed by experienced providers.

Magnetic Resonance Imaging (MRI)

Occasionally used when ultrasound findings are unclear or to evaluate for placenta accreta (abnormal placental attachment). Not routinely necessary for diagnosis.

Classification

Placenta previa is classified into four types:

  1. Complete previa: Placenta completely covers the cervical opening
  2. Partial previa: Placenta partially covers the cervical opening
  3. Marginal previa: Placental edge reaches the cervical opening but doesn't cover it
  4. Low-lying placenta: Placenta is within 2 cm of the cervix but doesn't reach it

Follow-up Monitoring

  • Serial ultrasounds to track placental position
  • Most cases diagnosed before 20 weeks resolve as the uterus grows
  • Persistence after 32 weeks usually indicates it will remain until delivery
  • Final determination typically made at 36 weeks for delivery planning

Treatment Options

Management of placenta previa depends on several factors including the type of previa, gestational age, presence of bleeding, and maternal and fetal condition. The primary goals are preventing hemorrhage and optimizing timing of delivery.

Conservative Management (No Active Bleeding)

Outpatient Management

For stable patients without bleeding:

  • Activity modification: Avoiding strenuous activities and heavy lifting
  • Pelvic rest: No sexual intercourse, douching, or vaginal examinations
  • Regular monitoring: Frequent prenatal visits and ultrasounds
  • Patient education: Warning signs and when to seek immediate care
  • Iron supplementation: To prevent anemia

Hospital Admission Criteria

  • Any episode of bleeding
  • Preterm contractions
  • Living far from medical facilities
  • Inability to maintain bed rest at home
  • Complete placenta previa after 30 weeks (controversial)

Management of Bleeding Episodes

Initial Stabilization

  • Hospitalization: Immediate admission for assessment
  • IV access: Large-bore IV lines for potential transfusion
  • Blood typing and cross-matching: Preparation for possible transfusion
  • Continuous fetal monitoring: Assessing fetal well-being
  • Maternal vital signs: Monitoring for signs of hemorrhage

Medical Interventions

  • Corticosteroids: Between 24-34 weeks to enhance fetal lung maturity
  • Tocolytics: May be used for preterm contractions if stable
  • Rh immunoglobulin: For Rh-negative mothers after bleeding
  • Blood products: Transfusion if significant blood loss

Delivery Planning

Timing of Delivery

  • Scheduled cesarean: Typically at 36-37 weeks for stable complete previa
  • Emergency delivery: For uncontrolled bleeding regardless of gestational age
  • Individual assessment: Based on bleeding episodes and fetal maturity

Delivery Preparation

  • Cesarean section: Required for complete and most partial previas
  • Blood products available: Cross-matched blood ready
  • Experienced team: Obstetric and anesthesia teams prepared
  • Neonatal team: Present for potential preterm delivery
  • Possible hysterectomy consent: In case of uncontrolled hemorrhage

Postpartum Care

  • Close monitoring for postpartum hemorrhage
  • Uterine massage and oxytocin to prevent bleeding
  • Serial hemoglobin checks
  • Early ambulation when stable
  • Counseling about recurrence risk in future pregnancies

Prevention

While placenta previa cannot always be prevented, certain measures may reduce risk or improve outcomes:

Risk Reduction Strategies

  • Smoking cessation: Ideally before conception
  • Avoid unnecessary cesarean sections: Opt for vaginal delivery when safe
  • Limit uterine procedures: Avoid elective surgeries on the uterus
  • Substance abuse treatment: Particularly cocaine cessation
  • Optimal pregnancy spacing: Allow adequate healing between pregnancies

Early Detection and Management

  • Regular prenatal care for early diagnosis
  • Inform providers of risk factors
  • Compliance with activity restrictions if diagnosed
  • Living near medical facilities in third trimester if diagnosed
  • Having a support system for potential bed rest

When to See a Doctor

Immediate medical attention is crucial for certain symptoms during pregnancy, especially with known or suspected placenta previa.

Seek Emergency Care Immediately For:

  • Any vaginal bleeding during pregnancy
  • Severe abdominal pain or cramping
  • Contractions before 37 weeks
  • Decreased or absent fetal movement
  • Dizziness, lightheadedness, or fainting
  • Rapid heartbeat or shortness of breath

Contact Your Healthcare Provider For:

  • Mild spotting or pink-tinged discharge
  • Increased pelvic pressure
  • Lower back pain that's new or worsening
  • Questions about activity restrictions
  • Concerns about fetal movement patterns

Important Reminders

  • Never ignore bleeding during pregnancy
  • Don't wait to see if bleeding stops on its own
  • Keep a record of bleeding episodes
  • Have transportation plans ready for emergencies

Related Conditions

Several conditions may occur with or be confused with placenta previa:

Frequently Asked Questions

Can placenta previa correct itself?

Yes, in many cases diagnosed early in pregnancy (before 20 weeks), the placenta appears to "move" away from the cervix as the uterus grows. About 90% of cases diagnosed in the second trimester resolve by the third trimester. However, placenta previa that persists into the third trimester is unlikely to resolve.

Can I have a vaginal delivery with placenta previa?

Complete placenta previa requires cesarean delivery as the placenta blocks the baby's exit. Partial previa also typically requires cesarean section. Only in cases of low-lying placenta where the edge is more than 2 cm from the cervix might vaginal delivery be considered, based on individual assessment.

Is bed rest necessary with placenta previa?

Complete bed rest is controversial and not always recommended. Most doctors advise "pelvic rest" (avoiding intercourse and vaginal exams) and activity modification rather than strict bed rest. The approach depends on the type of previa, presence of bleeding, and individual circumstances.

What are the chances of placenta previa recurring?

The recurrence rate is approximately 4-8%. Risk factors for recurrence include multiple cesarean sections, advanced maternal age, and smoking. Discuss your individual risk with your healthcare provider when planning future pregnancies.

Can I fly with placenta previa?

Air travel with placenta previa requires individual assessment. Generally, it's not recommended in the third trimester or if you've had bleeding episodes. The main concern is being far from medical care if bleeding occurs. Always consult your doctor before traveling.

References

  1. Silver RM. Abnormal Placentation: Placenta Previa, Vasa Previa, and Placenta Accreta. Obstet Gynecol. 2015;126(3):654-668.
  2. Jauniaux E, Alfirevic Z, Bhide AG, et al. Placenta Praevia and Placenta Accreta: Diagnosis and Management. BJOG. 2019;126(1):e1-e48.
  3. American College of Obstetricians and Gynecologists. Placenta Accreta Spectrum. Obstetric Care Consensus No. 7. Obstet Gynecol. 2018;132:e259-75.
  4. Cresswell JA, Ronsmans C, Calvert C, Filippi V. Prevalence of placenta praevia by world region: a systematic review and meta-analysis. Trop Med Int Health. 2013;18(6):712-724.
  5. Fan D, Wu S, Wang W, et al. Prevalence of placenta previa among deliveries: An update systematic review and meta-analysis. Arch Gynecol Obstet. 2021;303(4):935-945.
  6. Rosenberg T, Pariente G, Sergienko R, Wiznitzer A, Sheiner E. Critical analysis of risk factors and outcome of placenta previa. Arch Gynecol Obstet. 2011;284(1):47-51.

Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.