Causes of Vaginal Bleeding During Pregnancy
Vaginal bleeding during pregnancy occurs in approximately 25% of women and ranges from benign causes like implantation bleeding to life-threatening conditions such as placental abruption, ectopic pregnancy, and uterine rupture—with outcomes critically dependent on identifying the specific etiology through ultrasound evaluation. 1
Causes by Trimester
First Trimester (Most Common Period for Bleeding)
Physiologic causes:
- Implantation bleeding (normal spotting as embryo implants)
- "Bloody show" near term labor
Pathologic causes requiring urgent evaluation:
- Spontaneous abortion/miscarriage - occurs in approximately 50% of women who bleed in first trimester 2
- Ectopic pregnancy - prevalence up to 13% in symptomatic ED patients (much higher than general population) 3
- Subchorionic hematoma
- Gestational trophoblastic disease
- Anembryonic pregnancy/embryonic demise 2
Benign structural causes:
- Cervicitis
- Cervical polyps
- Vaginal lacerations
Second and Third Trimester
Critical diagnoses (can cause maternal/fetal death):
- Placenta previa - most common diagnosis, affects 1 in 200 pregnancies at delivery 1
- Placental abruption - affects ~1% of pregnancies; central abruption has worse perinatal outcomes than marginal separation 1
- Vasa previa - rare (1 in 2,500-5,000 deliveries) but can cause fetal exsanguination 1
- Uterine rupture - rare, most common in patients with prior cesarean delivery or uterine surgery 1
Other causes:
- Preterm labor with cervical bleeding
- Placenta accreta spectrum
- Cervical/vaginal lesions
Important note: Approximately 50% of women with vaginal bleeding in pregnancy have no identifiable cause 1
Evaluation Algorithm
Critical First Step
Avoid digital pelvic examination until placenta previa, low-lying placenta, and vasa previa are excluded by imaging 1
Imaging Approach (Based on ACR 2020 Guidelines)
Usually appropriate for ALL presentations:
- Transabdominal ultrasound of pregnant uterus 1
- Transvaginal ultrasound - safe and accurate even for placenta previa diagnosis; particularly helpful for cervical-related causes 1
- Duplex Doppler velocimetry 1
For first trimester specifically:
- Use discriminatory criteria: when β-hCG reaches 1,500-2,000 mIU/mL, normal pregnancy should show gestational sac on transvaginal ultrasound 2
- When gestational sac >10mm diameter, yolk sac must be present
- Live embryo must show cardiac activity when crown-rump length >5mm
- Normal β-hCG increases 80% every 48 hours 2
Transperineal ultrasound:
- May be appropriate for painless/painful bleeding
- Usually NOT appropriate for suspected placenta previa, low-lying placenta, or vasa previa 1
Clinical Pitfalls to Avoid
Ultrasound limitations: Placental abruption is only identified by ultrasound in at most 50% of cases (likely fewer) 1
Premature rupture of membranes: Limited evidence on whether transvaginal probe increases chorioamnionitis risk; one randomized trial of 92 patients found no increased risk, but apply caution 1
Heterotopic pregnancy risk: In patients with infertility treatment, identifying intrauterine pregnancy does NOT exclude ectopic pregnancy 3
Adnexal mass or free pelvic fluid = ectopic pregnancy until proven otherwise 2
Associated Adverse Outcomes
Maternal complications linked to bleeding:
- Gestational hypertension (14.5% in bleeding patients, p=0.038) 4
- Preeclampsia (10.9%, p=0.047) 4
- Post-delivery hemorrhage 5
Neonatal complications:
- Preterm birth (OR: 1.8) 6
- Low birth weight (OR: 2.0; 29.1% in one cohort) 5, 6
- NICU admissions (23.3% in bleeding patients) 5
- Respiratory distress 5
- Stillbirth (OR: 2.5) 6
Severity matters: Heavy bleeding directly correlates with worse outcomes—34.6% preterm birth rate vs. 70.7% term delivery rate with mild spotting 4