What is the difference between placenta previa and placental abruption (placenta abruptio) in pregnancy?

Placenta Previa vs. Placental Abruption: Key Differences

Placenta previa is an abnormal placental location where the placenta overlies the cervical os, while placental abruption is the premature separation of a normally implanted placenta from the uterine wall. These are fundamentally different pathologic processes with distinct presentations, mechanisms, and management approaches.

Anatomic Location and Pathophysiology

Placenta Previa:

• The placenta is abnormally implanted in the lower uterine segment, covering or lying near the internal cervical os 1, 2
• Occurs in approximately 1 in 200 pregnancies at delivery 2
• Results from abnormal placental implantation, not placental detachment 3
• Often diagnosed incidentally on routine ultrasound, with 42.3% present at 11-14 weeks but most resolving by 28 weeks 1

Placental Abruption:

• The placenta separates prematurely from its normal implantation site in the uterine wall 4
• Occurs in approximately 1% of pregnancies 5
• Results from rupture of maternal decidual arteries causing dissection at the decidual-placental interface, often preceded by acute vasospasm 6
• Represents impaired placentation with uteroplacental underperfusion and intrauterine hypoxia 6

Clinical Presentation

Placenta Previa:

• Typically presents with painless, bright red vaginal bleeding in the second or third trimester 3, 7
• Bleeding may be provoked by cervical examination or intercourse 7
• Fetal distress is uncommon unless massive hemorrhage occurs 5
• May be completely asymptomatic until delivery 1

Placental Abruption:

• Classically presents with painful vaginal bleeding accompanied by uterine tenderness and contractions 4, 6
• Clinical picture varies from asymptomatic (diagnosed only at delivery) to massive abruption with fetal death 6
• Causes uteroplacental insufficiency, ischemia, chronic hypoxemia, and potential fetal death 4
• Most common cause of serious vaginal bleeding in pregnancy 5

Diagnostic Approach

Placenta Previa:

• Transvaginal ultrasound is the gold standard with 90.7% sensitivity and 96.9% specificity 2, 8
• Digital pelvic examination must be absolutely avoided until placenta previa is excluded, as it can trigger catastrophic hemorrhage 1, 2, 8
• Doppler ultrasound helps identify vasa previa and assess placental blood flow 8

Placental Abruption:

• Diagnosis is always clinical, based on symptoms of bleeding, pain, and uterine tenderness 6
• Ultrasound has limited utility as it cannot reliably exclude abruption 6
• No clinically useful predictive biomarkers currently exist 6

Risk Factors

Placenta Previa:

• Prior cesarean delivery is the most significant risk factor, with risk increasing from 3% with no prior cesarean to 67% with five or more cesareans 2
• Advanced maternal age, pregnancy termination, intrauterine surgery, smoking, multifetal gestation, and increasing parity 7
• In vitro fertilization 1

Placental Abruption:

• Previous placental abruption is the strongest predictor (AOR = 2.72) 9
• Preeclampsia, preterm premature rupture of membranes, smoking, cocaine use, and trauma 9
• Maternal age ≥35 years, black race, low BMI, anemia, and inadequate prenatal care 9
• Strenuous exercise increases immediate risk 7.8-fold in the hour following activity 4

Management Differences

Placenta Previa:

• Women with asymptomatic previa before 28 weeks can continue moderate-to-vigorous physical activity, but should restrict activity after 28 weeks to low-intensity walking only 1, 2, 8
• Planned cesarean delivery at 34 0/7 to 35 6/7 weeks for uncomplicated cases 1, 2, 8
• Delivery must not be delayed beyond 36 weeks due to hemorrhage risk 2, 8
• Requires delivery at a level III or IV facility with blood banking and multidisciplinary team 8

Placental Abruption:

• Women diagnosed with abruption must immediately stop all moderate-to-vigorous physical activity due to high maternal and neonatal risks 4
• Management may require rapid operative delivery to prevent fetal death 5
• Timing depends on severity, fetal status, and maternal stability 6, 5

Critical Complications

Placenta Previa:

• Primary risk is massive maternal hemorrhage at delivery 2
• Placenta accreta spectrum disorder occurs in 3-67% depending on number of prior cesareans 2
• May require cesarean hysterectomy if accreta is present 1, 8

Placental Abruption:

• Causes fetal hypoxemia and potential fetal death from uteroplacental insufficiency 4
• Maternal complications include hemorrhagic shock and coagulopathy 6
• Larger abruptions lead to chronic hypoxemia and fetal demise 4

Common Pitfalls

• Never perform digital pelvic examination when placenta previa is suspected or not yet excluded—this can trigger life-threatening hemorrhage 1, 2, 8
• Do not rely on ultrasound to exclude placental abruption; diagnosis is clinical 6
• Failure to screen for placenta accreta spectrum in women with placenta previa and prior cesareans can lead to catastrophic intraoperative hemorrhage 1
• Habitual physical activity reduces abruption risk, but acute strenuous exercise increases immediate risk 4