8.3 Antepartum Haemorrhage: Placenta Praevia, Placental Abruption & Vasa Praevia
Key Takeaways
Antepartum haemorrhage (APH) is genital tract bleeding occurring from 24+0 weeks' gestation until birth, classified clinically as spotting, minor (<50 mL), major (50-1000 mL), or massive (>1000 mL or shock).
Placenta praevia presents with painless, bright red vaginal bleeding and a soft, non-tender uterus; digital vaginal examination is strictly contraindicated until ultrasound has definitively excluded praevia.
Placental abruption presents with severe, constant abdominal pain, dark vaginal bleeding (often concealed), a rigid 'woody' hard uterus, and fetal compromise, carrying severe risks of disseminated intravascular coagulation (DIC).
Vasa praevia involves unprotected fetal vessels traversing the membranes over the internal cervical os; rupture of membranes precipitates rapid fetal exsanguination with catastrophic bradycardia, demanding immediate category 1 caesarean section.
Major or massive APH requires immediate 2222 obstetric emergency activation, high-flow oxygen, two 14/16G IV cannulae, blood crossmatching (4-6 units), continuous CTG, and Kleihauer-Betke testing in RhD-negative women.
Antepartum Haemorrhage: Placenta Praevia, Placental Abruption & Vasa Praevia
Antepartum haemorrhage (APH) is defined as bleeding from or into the genital tract occurring from 24+0 weeks' gestation until the birth of the baby. APH complicates 3% to 5% of all pregnancies and represents a critical obstetric emergency associated with significant maternal morbidity, preterm birth, fetal hypoxia, and perinatal death. Clinical care in the UK is governed by the Royal College of Obstetricians and Gynaecologists (RCOG) Green-top Guideline No. 63 (Antepartum Haemorrhage).
Definition & Severity Classification of Antepartum Haemorrhage
Bleeding before 24+0 weeks is classified as threatened or inevitable miscarriage. From 24+0 weeks onwards, APH is stratified into four clinical severity tiers based on estimated blood loss and hemodynamic impact:
| Severity Tier | Estimated Blood Loss Volume | Clinical Features & Hemodynamic Presentation |
|---|---|---|
| Spotting | Staining, streaking, or blood spots | Minimal blood on underwear or sanitary towel; no hemodynamic compromise. |
| Minor Haemorrhage | <50 mL | Small volume loss that has settled; maternal vital signs completely stable. |
| Major Haemorrhage | 50–1000 mL | Substantial blood loss without clinical signs of maternal shock. |
| Massive Haemorrhage | >1000 mL or signs of shock | Extensive blood loss AND/OR clinical evidence of hemodynamic shock (tachycardia >100 bpm, hypotension, cold peripheries, pallor, oliguria, confusion). |
Important
Clinical estimation of external vaginal blood loss consistently underestimates true haemorrhage. In conditions such as placental abruption, massive haemorrhage can remain entirely concealed behind the placenta, causing profound maternal hypovolaemic shock and fetal demise without visible external blood loss.
Placenta Praevia & Low-Lying Placenta
Placenta praevia occurs when the placenta implants entirely or partially in the lower uterine segment. Under RCOG terminology (Green-top Guideline No. 27):
- Low-Lying Placenta: The lower placental edge lies within 20 mm (2.0 cm) of the internal cervical os on transvaginal ultrasound (TVS) in the third trimester, but does not cover it.
- Placenta Praevia: The placenta directly covers the internal cervical os.
1. Risk Factors & Placenta Accreta Spectrum
Primary predisposing factors include: previous caesarean birth (risk multiplies with each subsequent caesarean hysterotomy scar), advanced maternal age (≥35 years), multiparity, assisted reproductive technology (IVF), multiple pregnancy, maternal smoking, and previous uterine curettage.
When a placenta praevia implants over a previous anterior caesarean scar, the risk of placenta accreta spectrum (PAS)—where chorionic villi abnormally adhere to or invade through the myometrium—rises steeply with each previous caesarean (with praevia, about 40% after three previous caesareans and more than 60% after four or more), creating catastrophic intrapartum haemorrhage risks.
2. Clinical Presentation
- Haemorrhage: Painless, recurrent, bright red vaginal bleeding, often unprovoked and appearing spontaneously during rest or sleep.
- Abdominal Palpation: The uterus is soft, relaxed, and non-tender.
- Fetal Assessment: Fetal heart rate is usually normal and reassuring (unless maternal exsanguination causes terminal hypoperfusion).
- Lie and Presentation: The presenting part is characteristically high, floating, and unengaged, or there is an abnormal fetal lie (transverse lie, oblique lie, or breech presentation) because the low placental mass mechanically obstructs fetal engagement in the pelvic brim.
3. The Strict Contraindication to Digital Vaginal Examination
Warning
NEVER PERFORM A DIGITAL VAGINAL EXAMINATION (PV) in any pregnant woman presenting with antepartum haemorrhage until placental localisation has been confirmed by ultrasound! Inserting examining fingers through the cervix can detach placental cotyledons from the vascular lower uterine segment, triggering catastrophic, uncontainable arterial haemorrhage that can prove fatal within minutes.
4. Antenatal Management & Timing of Birth
Asymptomatic women with confirmed placenta praevia are scheduled for elective caesarean delivery between 36+0 and 37+0 weeks' gestation (with antenatal corticosteroids administered prior to delivery). Women with low-lying placenta (10–20 mm from os) can be counselled regarding trial of vaginal birth if the fetal head is engaged and no bleeding occurs, though senior obstetrician involvement is required.
Placental Abruption (Abruptio Placentae)
Placental abruption is defined as the premature separation of a normally situated placenta from the uterine decidua basalis prior to the birth of the baby.
1. Pathophysiology & Revealed vs. Concealed Haemorrhage
Rupture of maternal decidual spiral arterioles leads to bleeding into the decidua basalis. The expanding retroplacental haematoma cleaves the placental attachment from the uterine wall, shearing overlying villous capillaries and destroying maternal-fetal gas exchange.
- Revealed Haemorrhage (80% of cases): Blood dissects between the fetal membranes and uterine decidua, escaping through the cervix into the vagina. The blood is typically dark red or brown.
- Concealed Haemorrhage (20% of cases): The margins of the placenta remain adherent, or the fetal head tightly occludes the lower uterine segment, trapping the entire haematoma behind the placenta. Maternal shock and coagulopathy develop rapidly despite minimal or absent visible vaginal loss.
2. Etiology & Risk Factors
Key triggers include: maternal pre-eclampsia and chronic hypertension (accounting for >50% of severe abruptions), previous placental abruption (10-fold increased recurrence), abdominal trauma (domestic abuse, road traffic collisions), sudden uterine decompression (rapid release of polyhydramnios fluid or birth of a first twin), maternal cocaine or amphetamine misuse, smoking, and advanced parity.
3. Clinical Presentation
- Pain: Severe, continuous, agonizing abdominal or back pain with no pain-free interval.
- Uterine Examination: The uterus is characteristically described as "woody" hard, intensely hypertonic, and tender on palpation. Uterine contractions are frequent and low-amplitude, with elevated resting tone.
- Fetal Compromise: Severe fetal heart rate abnormalities: persistent baseline tachycardia, prolonged or late decelerations, loss of variability, sinusoidal pattern, or intrauterine fetal demise.
- Maternal Shock: Tachycardia, hypotension, and pallor out of proportion to visible blood loss.
- Disseminated Intravascular Coagulation (DIC): Massive retroplacental tissue destruction releases huge amounts of tissue thromboplastin into maternal circulation, activating systemic coagulation cascades. Clotting factors and platelets are consumed rapidly, resulting in severe hypofibrinogenaemia (<2.0 g/L) and intractable microvascular haemorrhage.
Vasa Praevia
Vasa praevia is an uncommon but catastrophic obstetric condition wherein unprotected fetal blood vessels traverse the fetal membranes across the internal cervical os, positioned below the fetal presenting part without the protection of the umbilical cord or Wharton's jelly.
1. Pathogenesis & Anatomy
Vasa praevia arises in two primary configurations: velamentous cord insertion (where umbilical vessels insert into membranes away from the placental disc) or succenturiate placental lobes (where connecting intercotyledonary vessels bridge two lobes across the os).
2. The Clinical Triad of Rupture
Vasa praevia remains asymptomatic until the fetal membranes rupture spontaneously or artificially (SROM or ARM). When the membranes tear, the traversing fetal vessels are lacerated, resulting in:
- Painless Vaginal Bleeding: Moderate, fresh vaginal bleeding occurring immediately at the moment of membrane rupture.
- Catastrophic Fetal Deterioration: Sudden, severe fetal bradycardia, prolonged variable decelerations, or a classical sinusoidal fetal heart rate pattern on cardiotocography.
- Normal Maternal Observations: Maternal vital signs, pulse, and blood pressure remain completely stable and unaffected, because the bleeding is entirely fetal.
Warning
At term, total fetoplacental blood volume is only 250 to 300 mL (80–90 mL/kg). A blood loss of merely 50 to 100 mL represents acute hypovolaemic shock and rapid exsanguination for the fetus. Vasa praevia diagnosed intrapartum requires an immediate Category 1 emergency caesarean section (delivery within 15–30 minutes) and immediate preparation for neonatal blood transfusion.
Comparison of Placenta Praevia, Abruption & Vasa Praevia
| Clinical Parameter | Placenta Praevia | Placental Abruption | Vasa Praevia |
|---|---|---|---|
| Nature of Bleeding | Painless, recurrent, bright red | Painful, constant, dark red (or concealed) | Painless, fresh bleeding immediately following membrane rupture |
| Uterine Tone & Palpation | Soft, relaxed, non-tender | "Woody" hard, hypertonic, intensely tender | Soft, normal resting tone between contractions |
| Fetal Heart Pattern | Generally normal / reassuring | Fetal distress, decelerations, or absent | Sudden severe bradycardia or sinusoidal FHR |
| Maternal Hemodynamics | Proportional to visible loss | Disproportionate shock (concealed loss) | Completely normal (bleeding is fetal) |
| Coagulopathy (DIC) | Rare (only after massive shock) | Common (thromboplastin release) | Absent |
| Digital Examination | Strictly contraindicated | Contraindicated until ultrasound excludes praevia | Contraindicated until ultrasound excludes praevia |
Immediate Clinical Management of Major/Massive APH
When a pregnant woman presents with major or massive APH, the midwife must coordinate an immediate multidisciplinary emergency response:
- Emergency Call (2222): Summon the obstetric emergency team: senior obstetrician, senior midwife, obstetric anaesthetist, haematologist, and neonatal resuscitation team.
- Resuscitation & Positioning: Position in left lateral tilt (15–30 degrees) to relieve aortocaval compression. Administer high-flow oxygen (15 L/min via non-rebreather mask).
- Intravenous Access: Secure two large-bore intravenous cannulae (14-gauge orange or 16-gauge grey) in the antecubital fossae.
- Laboratory Blood Investigations:
- Full Blood Count (FBC): Evaluate baseline haemoglobin, haematocrit, and platelets.
- Coagulation Profile: Prothrombin time (PT), activated partial thromboplastin time (APTT), and Fibrinogen (fibrinogen <2.0 g/L signals severe consumptive coagulopathy).
- Renal & Liver Function: Urea, creatinine, electrolytes, and transaminases.
- Group and Crossmatch: Crossmatch 4 to 6 units of packed red blood cells immediately. If un-crossmatched blood is needed for imminent arrest, request O-negative red cells.
- Kleihauer-Betke Test: Mandatory in all Rhesus D-negative women to quantify the volume of feto-maternal haemorrhage (FMH) and calculate the dose of Anti-D immunoglobulin required above standard routine prophylaxis (standard 500 IU covers up to 4 mL FMH; 125 IU per additional 1 mL fetal red cells).
- Fluid Resuscitation: Infuse up to 2,000 mL warmed crystalloids (Plasma-Lyte or 0.9% normal saline) while awaiting blood products. If bleeding is massive, activate the Massive Obstetric Haemorrhage Protocol (MOHP) to deliver red cells and, following the local protocol, fresh frozen plasma, platelets and fibrinogen replacement (cryoprecipitate or fibrinogen concentrate), guided by laboratory or point-of-care coagulation testing.
- Fetal Monitoring: Continuous electronic fetal monitoring (CTG) if gestational age ≥24 weeks and fetus alive.
- Expedited Delivery: Category 1 emergency caesarean birth is indicated for ongoing major/massive haemorrhage, maternal instability, placental abruption with fetal compromise, or vasa praevia.
A 31-year-old multigravida at 34 weeks' gestation attends the maternity triage unit with fresh, painless, bright red vaginal bleeding of approximately 150 mL. Abdominal palpation reveals a soft, non-tender, relaxed uterus with a high, floating fetal presenting part. The fetal heart rate is 140 beats per minute with normal variability on cardiotocography. Which condition is most strongly suspected, and what clinical examination is strictly contraindicated?
Placental abruption; speculum examination is contraindicated
Vasa praevia; abdominal ultrasound is contraindicated
Cervical ectropion; abdominal palpation is contraindicated
Placenta praevia; digital vaginal examination is strictly contraindicated
A woman at 36 weeks' gestation presents following a road traffic collision complaining of severe, continuous abdominal pain and dark vaginal spotting. On abdominal examination, the uterus is intensely tender and remains persistently contracted ('woody' hard) between palpations. Fetal monitoring shows persistent late decelerations with baseline tachycardia of 170 bpm. Maternal blood pressure is 95/55 mmHg and pulse is 118 bpm. What is the underlying pathophysiology and major maternal haematological risk?
Premature separation of the placenta with retroplacental haematoma and release of decidual thromboplastin, creating a high risk of Disseminated Intravascular Coagulation (DIC)
Rupture of fetal membranes over the cervical os with tearing of unsupported umbilical vessels and rapid fetal exsanguination
Abnormal implantation of the placenta covering the internal cervical os with painless disruption of maternal venous sinuses
Spontaneous rupture of the unscarred myometrium resulting in immediate expulsion of the fetus into the peritoneal cavity
A woman in labour at 39 weeks' gestation has spontaneous rupture of membranes. Immediately following the release of clear amniotic fluid, approximately 60 mL of fresh blood is noted at the vulva, and the cardiotocograph displays sudden, severe fetal bradycardia dropping to 70 beats per minute with loss of variability. Abdominal palpation reveals a soft uterus between contractions, and maternal vital signs remain completely stable (BP 118/76 mmHg, pulse 76 bpm). What is the definitive diagnosis and required emergency intervention?
Placental abruption; commence intravenous oxytocin infusion to expedite vaginal delivery
Severe placenta praevia; administer intramuscular ergometrine and perform an immediate artificial rupture of membranes
Vasa praevia; perform an immediate category 1 emergency caesarean section and prepare for neonatal resuscitation and blood transfusion
Rupture of the uterine scar; perform an emergency laparotomy under regional spinal anaesthesia
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