What are the differential diagnoses for a pregnant patient presenting with bleeding?

Differential Diagnoses for Bleeding During Pregnancy

The differential diagnosis for bleeding in pregnancy depends critically on gestational age, with first trimester bleeding most commonly caused by threatened abortion, early pregnancy loss, or ectopic pregnancy, while second and third trimester bleeding requires immediate consideration of placenta previa, placental abruption, and vasa previa—all of which can be life-threatening. 1, 2

First Trimester Bleeding (Up to 13 Weeks)

Most Common Diagnoses

• Threatened abortion occurs in 20-40% of pregnant women and represents bleeding with a closed cervix and viable intrauterine pregnancy 3, 4
• Early pregnancy loss (miscarriage) accounts for approximately 12% of recognized pregnancies and presents with bleeding that may be accompanied by cramping 1, 4
• Ectopic pregnancy occurs in 1-2% of pregnancies but accounts for 6% of maternal deaths, making it the most critical diagnosis to exclude 4, 5
• Pregnancy of unknown location represents 80-93% early intrauterine pregnancies or failed pregnancies, but 7-20% will ultimately be ectopic 1, 6

Less Common First Trimester Causes

• Subchorionic hemorrhage can be identified on ultrasound in viable pregnancies and requires follow-up imaging in 1-2 weeks 1
• Cervical lesions, polyps, or cervicitis cause spotting and are identified on speculum examination 1
• Implantation bleeding is physiologic and minimal in volume 3

Second and Third Trimester Bleeding (After 13 Weeks)

Life-Threatening Diagnoses (Must Exclude First)

• Placenta previa is the most common diagnosis in late pregnancy bleeding, affecting approximately 1 in 200 pregnancies at delivery, and presents with painless bright red bleeding 1, 2
• Placental abruption affects 1% of pregnancies and is the most common cause of serious vaginal bleeding, presenting with painful bleeding and potentially normal initial ultrasound (misses 50% of cases) 1, 2
• Vasa previa is rare but results in fetal exsanguination with membrane rupture and requires Doppler evaluation for vessels overlying the internal cervical os 1, 2
• Uterine rupture must be considered in patients with prior cesarean delivery, looking for myometrial disruption or lower uterine segment thickness <2.5 mm 1

Common Physiologic Causes

• "Bloody show" with term labor is normal physiologic bleeding characterized as pink or brown-tinged mucus, minimal in volume, and not soaking through pads 1, 7
• Cervical change with preterm labor can cause bleeding and requires cervical length assessment 1

Other Important Diagnoses

• Bleeding of unknown etiology accounts for approximately 50% of cases with vaginal bleeding in pregnancy after excluding other causes 1

Rare but Critical Systemic Causes (Any Trimester)

Cardiovascular Emergencies

• Amniotic fluid embolism presents with the classic triad of hypotension, hypoxia, and coagulopathy, with 70% occurring during labor 8, 7
• Myocardial infarction should be considered with risk factors including advanced maternal age, diabetes, chronic hypertension, smoking, and obesity 8
• Pulmonary embolism is a recognized pregnancy complication but unlikely if profuse bleeding is present 8

Hematologic Disorders

• Inherited bleeding disorders including von Willebrand disease (most common), hemophilia carriers, platelet disorders, and connective tissue disorders affect both maternal and fetal outcomes 9
• Disseminated intravascular coagulation may follow cardiovascular collapse and requires early assessment of clotting status 8

Critical Management Principles

Immediate Safety Steps

• Never perform digital pelvic examination before ultrasound in second or third trimester bleeding, as this can precipitate catastrophic hemorrhage if placenta previa or vasa previa is present 1, 7, 2
• Obtain transvaginal ultrasound as first-line diagnostic tool for first trimester bleeding, providing superior resolution compared to transabdominal approach 1, 6
• Measure quantitative beta-hCG regardless of ultrasound findings to help identify ectopic pregnancies and guide interpretation 1, 6

Diagnostic Pitfalls to Avoid

• Ultrasound can miss up to 74% of ectopic pregnancies initially, requiring serial beta-hCG monitoring when initial imaging is non-diagnostic 1, 6
• Normal vital signs do not exclude serious pathology, as placental abruption can present with normal hemodynamics initially but rapidly deteriorate 1, 7
• At very early gestations (3-5 weeks), gestational sac may be too small to visualize, requiring serial beta-hCG measurements every 48 hours until reaching discriminatory threshold of 1,500-2,000 mIU/mL 1, 6

Long-Term Implications

• First trimester bleeding increases risk of preterm delivery, placental abruption later in pregnancy, and small for gestational age infants even if pregnancy continues 1, 7
• Short cervix identified with bleeding significantly increases preterm delivery risk and requires close prenatal follow-up 1