What is the differential diagnosis for a pregnant female in her first trimester presenting with vaginal bleeding?

Differential Diagnosis for First Trimester Vaginal Bleeding

The most common differential diagnoses for first trimester vaginal bleeding include threatened abortion (viable intrauterine pregnancy with bleeding), early pregnancy loss/spontaneous abortion, ectopic pregnancy, subchorionic hematoma, gestational trophoblastic disease, and cervical lesions. 1

Most Common Diagnoses

Threatened Abortion (Most Common)

• Occurs in 7-27% of all pregnancies and represents the most frequent outcome when bleeding occurs in the first trimester 1
• Characterized by vaginal bleeding with a viable intrauterine pregnancy demonstrating fetal cardiac activity 1
• Ectopic pregnancy is essentially ruled out (except rare heterotopic pregnancy in <1% of spontaneous conceptions) once intrauterine pregnancy with fetal cardiac activity is confirmed 1, 2

Early Pregnancy Loss/Spontaneous Abortion

• Overall miscarriage risk is approximately 12% in patients presenting with first trimester bleeding 1
• Includes embryonic demise, anembryonic pregnancy, and incomplete abortion 3
• About one half of patients who experience first trimester bleeding will ultimately miscarry 3

Ectopic Pregnancy (Critical to Exclude)

• Occurs in 7-20% of pregnancy of unknown location cases 1, 2
• Ultrasound initially misses up to 74% of ectopic pregnancies, making serial beta-hCG monitoring absolutely critical when initial ultrasound is non-diagnostic 1, 2
• Presence of an adnexal mass or free pelvic fluid represents ectopic pregnancy until proven otherwise 3

Other Important Diagnoses

Subchorionic Hematoma

• Present in approximately 20% of women with first trimester bleeding 4
• Occurs with viable pregnancy and requires documentation of location relative to the placenta 4
• Managed with follow-up ultrasound in 1-2 weeks if pregnancy remains viable 1, 2

Gestational Trophoblastic Disease

• Less common but important to exclude 1
• Must be surgically evacuated rather than managed medically 3
• Doppler ultrasound may be helpful as an ancillary tool in management 5

Cervical Lesions and Local Causes

• Includes cervical polyps, cervicitis, cervical lesions, and infections 1, 6
• Identified after ultrasound excludes more serious pathology 1
• Diagnosed through speculum examination once placental causes are excluded 2

Rare but Important Diagnoses

Uterine Arteriovenous Malformation

• Can present with first trimester bleeding, though terminology is evolving 5
• Many are not true AVMs and will resolve spontaneously 5
• Doppler imaging is important for diagnosis, though grayscale ultrasound may show suggestive findings 5

Implantation Bleeding

• Physiologic bleeding that can occur in early pregnancy 6
• Diagnosis of exclusion after more serious pathology is ruled out 6

Critical Diagnostic Pitfalls

• Most pregnancies of unknown location (80-93%) will be early intrauterine or failed intrauterine pregnancies, but 7-20% will be ectopic, requiring vigilant follow-up 1, 2
• Avoid overinterpretation of a single ultrasound that could lead to inappropriate treatment with methotrexate or dilation and curettage, potentially harming a normal early pregnancy 1
• Never perform digital pelvic examination before ultrasound imaging, as this can precipitate catastrophic hemorrhage if placental abnormalities exist 1, 2

Prognostic Considerations

• First trimester bleeding increases risk of preterm delivery, placental abruption, and small for gestational age infants if pregnancy continues 1, 2
• The amount of bleeding and associated symptoms such as nausea and vomiting can have prognostic value 7