12.3 Antepartum Haemorrhage: Placenta Previa & Abruptio Placentae
Key Takeaways
- Antepartum haemorrhage (APH) is defined as bleeding from or into the genital tract after 28 completed weeks of pregnancy prior to delivery.
- Placenta Previa presents with painless, causeless, recurrent bright red vaginal bleeding; digital vaginal examination is strictly contraindicated due to risk of fatal hemorrhage.
- Abruptio Placentae presents with painful, dark red bleeding, a woody hard tender uterus, high association with maternal hypertension, and risk of Couvelaire uterus and DIC.
- Transvaginal ultrasonography is the gold standard for diagnosing placenta previa, while Macafee and Johnson protocol guides conservative management in preterm stable cases.
- Vasa Previa is characterized by the triad of membrane rupture, painless vaginal bleeding, and fetal bradycardia, diagnosed using the Apt (NaOH) test.
12.3 Antepartum Haemorrhage: Placenta Previa & Abruptio Placentae
Antepartum Haemorrhage (APH) is defined as bleeding from or into the genital tract after 28 completed weeks of gestation (the threshold of fetal viability in India) up to the time of delivery of the fetus. APH affects 3–5% of all pregnancies and demands rapid clinical diagnosis and targeted intervention to prevent maternal hemorrhagic shock and fetal demise.
1. Classification & Etiology of APH
Major causes of antepartum hemorrhage are categorized into:
- Placenta Previa (~35%): Bleeding due to placental implantation in the lower uterine segment.
- Abruptio Placentae (~30%): Premature separation of a normally implanted placenta.
- Extraplacental Causes (~5%): Cervical lesions (ectropion, cervical polyp, cervical carcinoma), vaginitis, local genital trauma.
- Unexplained / Indeterminate (~30%): Marginal sinus rupture or localized retroplacental bleeding not meeting criteria for major abruption.
2. Placenta Previa
Placenta Previa occurs when the placenta implants partially or wholly over the lower uterine segment (in close proximity to or covering the internal cervical os).
Etiology & Risk Factors
- Prior Cesarean Section: The single most potent risk factor. Risk increases exponentially with the number of prior uterine scars (1 prior CS: 0.65% risk; 4 prior CS: 10% risk). Strongly linked to Placenta Accreta Spectrum (PAS).
- Advanced maternal age ($>35\text{ years}$).
- High multiparity.
- Prior uterine curettage or myomectomy.
- Multiple pregnancy (larger placental surface area).
- Maternal cigarette smoking.
Anatomical Degrees / Types
| Type | Name | Anatomical Relationship to Internal Cervical Os |
|---|---|---|
| Type I | Low-Lying Placenta | Placental lower margin is in lower uterine segment but does not reach internal os ($< 2\text{ cm}$ from os) |
| Type II | Marginal Placenta | Placenta reaches the margin of the internal os but does not cover it |
| Type III | Partial / Incomplete | Placenta covers internal os when closed, but not when dilated |
| Type IV | Complete / Total Central | Placenta completely covers the internal os even when fully dilated |
Type II Anterior vs. Type II Posterior (Stallworthy's Sign): Type II Anterior is safe for trial of labor. Type II Posterior is known as the "Dangerous Placenta Previa." As the fetal head descends into the pelvic brim, it compresses the posterior low-lying placenta against the sacral promontory, compromising fetal umbilical blood flow and precipitating acute fetal distress or fetal demise.
Clinical Presentation
- Classical Triad: Painless, Causeless, Recurrent, Bright Red vaginal bleeding.
- Abdominal Examination: Uterus is soft, relaxed, non-tender. Fundal height corresponds to gestational age. Fetal parts are easily palpable. Malpresentations (breech, transverse lie, oblique lie) and a high, unengaged presenting part are frequently present.
Diagnostic Golden Rules
- Gold Standard: Transvaginal Ultrasonography (TVS) is accurate, safe, and superior to transabdominal ultrasound for evaluating the exact distance between the placental edge and the internal os.
- CRITICAL CONTRAINDICATION: Digital vaginal examination (Per Vaginam / PV exam) is STRICTLY CONTRAINDICATED in any woman presenting with APH until placenta previa has been definitively excluded by ultrasound! A digital exam can tear the placental attachment and provoke catastrophic, fatal hemorrhage.
Management Protocols
- Macafee and Johnson Conservative Management:
- Indications: Gestation $< 37\text{ weeks}$, bleeding mild or stopped, mother hemodynamically stable, fetus alive without distress.
- Protocol: Strict bed rest, cross-matched blood on standby, administration of antenatal corticosteroids (Betamethasone 12 mg IM 2 doses 24 hours apart) if $< 34\text{ weeks}$ for fetal lung maturity.
- Definitive Delivery Indications: Active heavy bleeding, gestation $\ge 37\text{ weeks}$, labor, or fetal distress.
- Mode of Delivery:
- Vaginal Delivery Trial: Type I and Type II Anterior (if placental edge is $> 2\text{ cm}$ from os).
- Cesarean Section: Absolute indication for Type II Posterior, Type III, and Type IV placenta previa.
3. Abruptio Placentae (Placental Abruption)
Abruptio Placentae is the premature detachment of a normally implanted placenta from the uterine wall after 28 weeks of gestation and before the delivery of the fetus.
Risk Factors
- Maternal Hypertensive Disorders: Pre-eclampsia, chronic hypertension (accounts for $> 50\text{ %}$ of severe cases; #1 risk factor).
- Sudden uterine decompression (e.g., rapid drainage of polyhydramnios, delivery of first twin).
- External abdominal trauma (motor vehicle accident, domestic violence).
- Short umbilical cord.
- Maternal cocaine abuse, tobacco smoking, thrombophilias.
Clinical Types
- Revealed Abruption (80%): Blood escapes through the cervix and drains externally. Pain and dark blood present.
- Concealed Abruption (20%): Blood accumulates behind the detached placenta (retroplacental hematoma) without external bleeding. Severe abdominal pain, uterine hypertonus, and maternal shock disproportionate to visible blood loss.
- Mixed Abruption: Combination of revealed and concealed components.
Clinical Features & Pathology
- Clinical Presentation: Painful, Dark Red vaginal bleeding accompanied by continuous severe abdominal or lower back pain.
- Abdominal Examination: Uterus is woody hard, board-like rigid, extremely tender. Fundal height may increase progressively in concealed abruption. Fetal parts are difficult to palpate due to uterine hypertonus. Fetal heart rate is often absent (fetal demise in ~20–30%) or exhibits severe late decelerations.
Severe Complications
- Couvelaire Uterus (Uteroplacental Apoplexy): Massive extravasation of blood into the uterine myometrium beneath the serosal perimetrium, extending into the broad ligaments. The uterus appears dark purplish/bluish mottled. It leads to severe myometrial atony and postpartum hemorrhage (PPH).
- Disseminated Intravascular Coagulation (DIC): Release of placental tissue thromboplastin into maternal circulation activates extrinsic coagulation cascade. Characterized by low fibrinogen ($< 150\text{ mg/dL}$), low platelets, and elevated D-dimer.
- Acute Kidney Injury (AKI): Caused by severe hypovolemic shock and acute tubular/cortical necrosis.
4. Differential Diagnosis: Placenta Previa vs. Abruptio Placentae
| Clinical Parameter | Placenta Previa | Abruptio Placentae |
|---|---|---|
| Nature of Bleeding | Painless, causeless, recurrent, bright red | Painful, associated with trauma/HTN, dark red |
| Uterine Tone | Soft, relaxed, normal tone | Board-like rigid, woody hard, hypertonic |
| Uterine Tenderness | Absent | Markedly tender |
| Fetal Palpation | Fetal parts easily felt; malpresentation common | Fetal parts difficult to feel |
| Fetal Heart Sounds | Usually normal and present | Often absent or severe fetal distress |
| Hypertension Association | Unrelated | Strongly associated ($> 50\text{ %}$) |
| Coagulopathy (DIC) | Rare | Common (especially in concealed type) |
5. Vasa Previa
Vasa Previa occurs when fetal blood vessels run unprotected by Wharton's jelly or placental tissue through the fetal membranes across the internal cervical os, ahead of the presenting fetal part. It is commonly associated with velamentous cord insertion or a succenturiate placental lobe.
Diagnostic Triad & Test
- Classic Triad: Rupture of membranes (spontaneous or artificial) $\rightarrow$ Painless vaginal bleeding $\rightarrow$ Rapid fetal bradycardia / asphyxia / death (because the bleeding is pure fetal blood).
- Diagnostic Apt Test (NaOH Test): Distinguishes fetal hemoglobin ($HbF$) from maternal hemoglobin ($HbA$). Addition of $1\text{ mL}$ of $1\text{ %}$ Sodium Hydroxide ($NaOH$) to $4\text{ mL}$ of blood solution:
- Fetal Blood: Remains PINK (alkali-resistant $HbF$).
- Maternal Blood: Turns BROWN-YELLOW (alkali-labile $HbA$).
A 29-year-old G3P2 woman at 32 weeks of gestation arrives at the labor room complaining of sudden, unprovoked, bright red vaginal bleeding. She denies any abdominal pain or contractions. On examination, her uterus is soft, non-tender, and fundal height corresponds to 32 weeks. Fetal heart rate is 142 bpm. Which of the following is the most appropriate next step in management?
A 32-year-old multiparous woman with a history of two prior Cesarean deliveries is diagnosed with a marginal placenta previa at 34 weeks. Ultrasound demonstrates that the placenta is located on the posterior wall of the lower uterine segment, encroaching on the internal os (Type II Posterior). Why is this specific type known as the 'Dangerous Placenta Previa'?
A 30-year-old G2P1 woman at 35 weeks of gestation with severe preeclampsia presents with sudden severe abdominal pain and dark vaginal bleeding. Examination reveals a board-like, rigid, tender uterus. Following delivery of a stillborn infant, the operating surgeon observes dark purplish discoloration and ecchymosis extending across the entire myometrium under the uterine serosa. What is the diagnosis for this uterine condition?
Following artificial rupture of membranes in a patient in active labor, there is sudden onset of painless vaginal bleeding accompanied by severe fetal bradycardia. Vasa previa is suspected. Which laboratory test on the vaginal blood specimen will confirm the presence of fetal blood?