What are the causes and management of bleeding in a female patient of childbearing age in her first trimester of pregnancy?

Causes of Bleeding in Early Pregnancy

First trimester bleeding occurs in 7-27% of pregnancies and most commonly represents threatened abortion (viable intrauterine pregnancy with bleeding), but ectopic pregnancy—the leading cause of maternal death in the first trimester—must be excluded in every case. 1, 2

Primary Causes by Frequency and Clinical Significance

Most Common Causes

• Threatened abortion is the most frequent diagnosis when an intrauterine pregnancy with fetal cardiac activity is confirmed on ultrasound, though it increases risk of preterm delivery, placental abruption, and small-for-gestational-age infants 2
• Early pregnancy loss/spontaneous abortion occurs in approximately 12% of pregnancies presenting with first trimester bleeding 2
• Subchorionic hematoma with viable pregnancy can be identified on ultrasound and requires follow-up imaging in 1-2 weeks 2

Life-Threatening Causes Requiring Immediate Exclusion

• Ectopic pregnancy occurs in 7-20% of pregnancy of unknown location cases and remains the most common cause of maternal death in the first trimester 1, 2
• Ectopic pregnancy prevalence reaches 13% in symptomatic ED patients, far higher than the general population 1

Less Common but Important Causes

• Gestational trophoblastic disease is less common but must be excluded through ultrasound evaluation 2
• Cervical lesions, polyps, or cervicitis are identified after ultrasound excludes more serious pathology 2
• Uterine arteriovenous malformation can present with first trimester bleeding, requiring Doppler imaging for diagnosis, though many resolve spontaneously 2

Diagnostic Algorithm

Immediate Initial Steps

• Assess hemodynamic stability first by checking for lightheadedness or dizziness suggesting significant blood loss 3, 4
• Obtain quantitative beta-hCG level immediately regardless of ultrasound findings to help identify ectopic pregnancies and guide interpretation 2, 4
• Perform transvaginal ultrasound before any digital pelvic examination, as this provides superior resolution and prevents catastrophic hemorrhage if placental abnormalities exist 2, 4

Critical Safety Rule

Never perform digital pelvic examination before ultrasound imaging in any pregnant patient with bleeding, as this can precipitate catastrophic hemorrhage if placenta previa, vasa previa, or other placental abnormalities are present. 3, 2, 4

Ultrasound Interpretation and Next Steps

If intrauterine pregnancy with fetal cardiac activity is confirmed:

• Ectopic pregnancy is essentially ruled out (except rare heterotopic pregnancy in <1% of spontaneous conceptions) 2, 4
• Assess for subchorionic hematoma presence 2
• Schedule follow-up ultrasound in 1-2 weeks to monitor progression 2
• Counsel that first trimester bleeding increases risk of preterm delivery, placental abruption, and small-for-gestational-age infants 2

If no intrauterine pregnancy is visualized (pregnancy of unknown location):

• Serial beta-hCG measurements every 48 hours are required until diagnosis is established 2, 4
• Repeat transvaginal ultrasound when beta-hCG reaches discriminatory threshold of 1,500-2,000 mIU/mL 2
• Gynecology referral for close monitoring is mandatory, as 7-20% will be ectopic pregnancies 2, 4
• Most pregnancies of unknown location (80-93%) will be early intrauterine or failed intrauterine pregnancies 2

If ectopic pregnancy is suspected or confirmed:

• Immediate specialist consultation is required 2

Additional Testing

• Complete blood count to assess hemoglobin if bleeding is moderate to heavy 2

Critical Pitfalls to Avoid

• Ultrasound misses up to 74% of ectopic pregnancies initially, making serial beta-hCG monitoring absolutely critical when initial ultrasound is non-diagnostic 2, 4
• Do not overinterpret a single ultrasound that could lead to inappropriate treatment with methotrexate or dilation and curettage, potentially harming a normal early pregnancy 2
• Never assume normal vital signs exclude serious pathology, as placental abruption can present with normal hemodynamics initially but rapidly deteriorate 3
• Avoid performing digital cervical examination before ultrasound if bleeding increases, as this can precipitate catastrophic hemorrhage if placenta previa or vasa previa is present 3, 4

Warning Signs Requiring Immediate Evaluation

• Bright red blood that flows continuously or soaks through pads (versus normal pink or brown-tinged mucus) 3
• Passage of clots 3
• Severe abdominal pain accompanying bleeding, which may indicate placental abruption 3
• Lightheadedness or dizziness suggesting significant blood loss 3
• Decreased fetal movement indicating compromised placental perfusion 3