Etiology and Pathogenesis of Placental Abruption
Pathophysiology
Placental abruption results from the premature separation of the normally implanted placenta from the uterine wall before fetal delivery, driven by both chronic decidual/uteroplacental vasculopathy and acute mechanical shearing forces. 1
The underlying mechanism involves:
- Decidual and endometrial-myometrial interface defects that lead to abnormal placental implantation and increased vulnerability to separation 2
- Uteroplacental vasculopathy causing chronic ischemia and weakening of the placental-uterine attachment 1
- Acute shearing forces applied to the abdomen (from trauma) that mechanically disrupt the placental attachment 1
- Hemorrhage into the decidua basalis that creates a retroplacental hematoma, further separating the placenta from the uterine wall and causing uteroplacental insufficiency, ischemia, and chronic hypoxemia 2
Epidemiology
- Incidence: Placental abruption affects approximately 0.4% to 1.2% of all pregnancies, with nearly half occurring at term gestations 2, 3, 1
- Mortality impact: It remains a leading cause of perinatal mortality and morbidity, particularly when involving more than 50% of the placenta 3
Risk Factors
Major Risk Factors (Strongest Associations):
- Prior placental abruption - the single strongest predictor of recurrence 3
- Hypertensive disorders including chronic hypertension and preeclampsia 3, 4
- Abdominal trauma - associated with a three-fold increase in perinatal mortality (25% vs 7% in non-trauma cases) 4
- Cocaine use and other substance abuse 3, 4
- Cigarette smoking (particularly ≥20 cigarettes per day) 2, 3
Additional Risk Factors:
- Advanced maternal age 3
- Multiparity and high gravidity 3
- Preterm premature rupture of membranes (pPROM) 3, 5
- Multifetal gestation 3
- Thrombophilias 3
- Intrauterine infections 3
- Hydramnios 3
- Placenta previa 5
- Uterine malformations 5
Clinical Presentation
The classic triad includes:
- Vaginal bleeding (though concealed hemorrhage can occur) 2, 1
- Abdominal pain with uterine tenderness 2, 1
- Abnormal fetal heart rate patterns ranging from tachycardia to bradycardia and fetal demise 1, 6
Important Caveat:
Ultrasound diagnosis is highly limited - identifying at most 50% of abruption cases, and likely far fewer. 2 The diagnosis remains primarily clinical based on history and physical examination findings 3, 6
Prognostic Factors
- Gestational age at delivery: Perinatal mortality is 42% when delivery occurs before 30 weeks versus 15% after 30 weeks 4
- Location of separation: Central abruption carries worse perinatal outcomes than marginal placental separation 2
- Extent of separation: Abruption involving >50% of the placenta is frequently associated with fetal death 3
- Birth weight: Lower birth weight correlates with increased perinatal mortality 4