What are the causes, diagnosis, and management of vaginal bleeding in pregnancy?

Vaginal Bleeding in Pregnancy: Causes, Diagnosis, and Management

Critical Safety Rule: Never Perform Digital Examination Before Ultrasound

Digital pelvic examination is absolutely contraindicated until ultrasound has definitively excluded placenta previa, low-lying placenta, and vasa previa, as examination before imaging can precipitate catastrophic hemorrhage. 1, 2, 3

---

CAUSES

First Trimester (< 13 weeks)

Pregnancy-Related:

• Threatened abortion with viable intrauterine pregnancy (fetal cardiac activity present on ultrasound) 2
• Ectopic pregnancy - affects 7-20% of pregnancies of unknown location 1, 2
• Spontaneous abortion (embryonic demise, anembryonic pregnancy, incomplete abortion) 4, 5
• Gestational trophoblastic disease (molar pregnancy) with abnormally elevated beta-hCG 2
• Subchorionic hemorrhage in viable pregnancy 1

Non-Pregnancy Related:

• Cervicitis, cervical polyps, or cervical lesions 1, 4
• Hormonal contraceptives (particularly progestin-only methods) causing irregular bleeding 2

Second and Third Trimester (≥ 13 weeks)

Life-Threatening Causes:

• Placenta previa - most common diagnosis in late pregnancy bleeding, affecting 1 in 200 pregnancies at delivery; presents as painless bleeding 1, 2, 6
• Placental abruption - affects approximately 1% of pregnancies; most common cause of serious vaginal bleeding; presents with abdominal pain and bleeding 1, 2, 6
• Vasa previa - rare but can result in fetal exsanguination with rupture of membranes 1, 6
• Uterine rupture - particularly in patients with prior cesarean delivery 1

Physiologic:

• "Bloody show" with term labor - normal physiologic bleeding characterized as pink or brown-tinged mucus, minimal in volume 1
• Cervical change with preterm labor 1

Unexplained:

• Approximately 50% of vaginal bleeding in pregnancy has no identifiable cause 1

---

DIAGNOSIS

Immediate Assessment Algorithm

Step 1: Assess Hemodynamic Stability

• Check vital signs immediately; clinically unstable patients may require urgent procedural management 3
• Recognize that normal vital signs do not exclude significant placental pathology such as placental abruption 1

Step 2: Obtain Laboratory Studies

• Quantitative beta-hCG level regardless of ultrasound findings 1, 3
• Complete blood count to assess hemoglobin and monitor trajectory 1
• Rh factor to determine need for anti-D immunoglobulin 7
• Coagulation panel including fibrinogen (fibrinogen < 200 mg/dL is an adverse factor requiring 24-hour observation) 7

Step 3: Ultrasound Evaluation (BEFORE Any Digital Examination)

First Trimester Approach:

• Transvaginal ultrasound is the primary diagnostic tool, providing superior resolution compared to transabdominal ultrasound 1, 3
• Assess for intrauterine pregnancy, ectopic pregnancy, or nonviable pregnancy 1
• Discriminatory threshold: At beta-hCG 1,500-2,000 mIU/mL, a normal intrauterine pregnancy must show a gestational sac on transvaginal ultrasound 1, 5, 8
• When gestational sac > 10 mm diameter, a yolk sac must be present 5
• When crown-rump length > 5 mm, cardiac activity must be present 5

Second/Third Trimester Approach:

• Transabdominal and transvaginal ultrasound with Doppler 1
• Assess placental location and exact distance from internal cervical os 1
• Evaluate for placental abruption (though ultrasound misses up to 50% of cases) 1, 2
• Doppler evaluation for vasa previa - vessels overlying internal cervical os can be subtle 1
• Cervical length assessment - short cervix with bleeding significantly increases preterm delivery risk 1
• Assess for uterine rupture in patients with prior cesarean (look for lower uterine segment thickness < 2.5 mm) 1

Step 4: Speculum Examination (When Safe)

• Assess for cervical lesions, polyps, or inflammation 1
• In cases of vaginal bleeding at or after 23 weeks, defer speculum or digital examination until placenta previa is excluded by ultrasound 7

Step 5: Fetal Monitoring (If Viable Pregnancy ≥ 23 weeks)

• All pregnant trauma patients with viable pregnancy should undergo electronic fetal monitoring for at least 4 hours 7
• Extend to 24-hour observation if adverse factors present: uterine tenderness, significant abdominal pain, vaginal bleeding, sustained contractions (> 1/10 min), rupture of membranes, atypical fetal heart rate pattern, high-risk mechanism, or fibrinogen < 200 mg/dL 7

Interpretation of Findings

Intrauterine Pregnancy Confirmed:

• If fetal cardiac activity present, ectopic pregnancy is essentially ruled out (except rare heterotopic pregnancy) 1, 3
• Evaluate for subchorionic hemorrhage 1

Pregnancy of Unknown Location:

• 80-93% will be early intrauterine pregnancies or failed intrauterine pregnancies 1
• 7-20% will later be diagnosed as ectopic pregnancies 1, 2
• Serial beta-hCG measurements every 48 hours - in normal pregnancy, levels increase by 80% every 48 hours 1, 5
• Repeat ultrasound when beta-hCG reaches discriminatory zone 1, 3

Critical Diagnostic Pitfalls:

• Ultrasound misses up to 50% of placental abruptions and 74% of ectopic pregnancies initially, which is why serial beta-hCG monitoring is critical when initial ultrasound is non-diagnostic 1
• Management of suspected placental abruption should not be delayed pending ultrasound confirmation as ultrasound is not sensitive for diagnosis 7

---

MANAGEMENT

First Trimester Management

Viable Intrauterine Pregnancy with Subchorionic Hemorrhage:

• Schedule follow-up ultrasound in 1-2 weeks 1, 3
• If hemoglobin drops (e.g., to 96 g/L), consider oral iron supplementation 1
• Transfusion not indicated unless patient is symptomatic or actively hemorrhaging 1

Pregnancy of Unknown Location:

• Serial beta-hCG measurements every 48 hours 1, 3
• Repeat ultrasound when beta-hCG reaches 1,500-2,000 mIU/mL 1, 8
• Continue serial measurements until diagnosis is established 1
• Maintain high clinical suspicion as 7-20% will be ectopic pregnancies requiring intervention 1, 3

Early Pregnancy Loss (Confirmed):

• Options include expectant, medical (misoprostol), and surgical management for hemodynamically stable patients 5, 8
• Exception: gestational trophoblastic disease must be surgically evacuated 5

Ectopic Pregnancy:

• Management options: surgical (laparoscopy), medical (methotrexate), or expectant in certain circumstances 5, 8

Second and Third Trimester Management

Placenta Previa/Low-Lying Placenta:

• Asymptomatic previa before 20 weeks: continue normal activities with repeat ultrasound at 28 weeks (nearly 90% ultimately resolve) 6
• Persistent previa in third trimester: pelvic rest mandated 6
• Significant bleeding: hospitalization required 6
• Transvaginal ultrasound is safe even with placenta previa and provides superior visualization 1

Placental Abruption:

• May require rapid operative delivery to prevent neonatal morbidity and mortality 6
• Maintain high clinical suspicion even with negative ultrasound 1

Vasa Previa:

• Risk of fetal exsanguination with rupture of membranes 6
• Requires urgent obstetrical consultation 3

General Management for Significant Bleeding:

• Rapid assessment of maternal and fetal status 6
• Fluid resuscitation with two large bore (14-16 gauge) IV lines 7
• Replacement of blood products when necessary 6
• For Rh-negative mothers: transfuse O-negative blood until cross-matched blood available 7
• Vasopressors only for intractable hypotension unresponsive to fluid resuscitation (adverse effect on uteroplacental perfusion) 7
• After mid-pregnancy: manual displacement of uterus or left lateral tilt to move gravid uterus off inferior vena cava 7
• Appropriately timed delivery 6

Rh Immunization Prevention

All Rh-Negative Pregnant Trauma/Bleeding Patients:

• Give anti-D immunoglobulin 7
• Perform Kleihauer-Betke test to quantify maternal-fetal hemorrhage and determine need for additional doses 7

Transfer Decisions

Viable Fetus (≥ 23 weeks) with Non-Life/Limb-Threatening Injuries:

• Transfer to maternity facility (labor and delivery triage) 7

Fetus < 23 weeks or Non-Viable:

• Transfer to emergency room 7

Major Injury:

• Transfer to trauma unit or emergency room regardless of gestational age 7

Long-Term Considerations

First Trimester Bleeding (Even if Pregnancy Continues):

• Increased risk of preterm delivery, placental abruption later in pregnancy, and small for gestational age infants 1
• Short cervix on transvaginal ultrasound with bleeding significantly increases preterm delivery risk 1

Placental Abruption:

• Recurrence risk in subsequent pregnancies, increased risk of stillbirth, and potential for fetal growth restriction 1