Causes of Early Pregnancy Bleeding
Early pregnancy bleeding (occurring in 20-40% of pregnancies) is most commonly caused by threatened miscarriage, early pregnancy loss, and ectopic pregnancy, with approximately 50% of cases having no identifiable cause even after thorough evaluation. 1, 2, 3
First Trimester Causes (Most Common)
Life-Threatening Conditions (Must Exclude First)
- Ectopic pregnancy occurs in 1-2% of pregnancies and accounts for 6% of all maternal deaths, making it the most critical diagnosis to exclude 3
- Miscarriage complications including threatened abortion, incomplete abortion, and missed abortion represent the majority of diagnosed cases 2, 3
- Approximately 7-20% of pregnancies of unknown location on initial ultrasound will ultimately be diagnosed as ectopic 1
Common Benign Causes
- Subchorionic hemorrhage is a frequent finding on ultrasound in viable pregnancies with bleeding 1
- Implantation bleeding occurs as the embryo attaches to the uterine wall 4
- Cervical causes including cervicitis, cervical polyps, or cervical lesions can produce spotting 1
Rare First Trimester Causes
- Gestational trophoblastic disease (molar pregnancy) is an uncommon but important diagnosis 4
Second and Third Trimester Causes
Painless Bleeding
- Placenta previa is the most common diagnosis in late pregnancy bleeding, affecting approximately 1 in 200 pregnancies at delivery 1
- Vasa previa involves fetal vessels overlying the internal cervical os and carries risk of fetal exsanguination 1
- "Bloody show" with term labor is normal physiologic bleeding characterized as pink or brown-tinged mucus, minimal in volume 1, 5
Painful Bleeding
- Placental abruption affects approximately 1% of pregnancies and is one of the leading causes of vaginal bleeding in the second half of pregnancy, accounting for 10% of all preterm births and 10-20% of perinatal deaths 1, 6
- Preterm labor with cervical change can cause bleeding 1
- Uterine rupture is particularly important in patients with prior cesarean delivery 1
Second Trimester Specific
- Incompetent cervix is the usual cause of second-trimester bleeding 4
Bleeding of Unknown Etiology
Approximately 50% of women with vaginal bleeding in pregnancy will have no identifiable cause after complete evaluation, highlighting the limitations of current diagnostic capabilities 1
Critical Diagnostic Pitfalls to Avoid
- Never perform digital vaginal examination before ultrasound in any pregnant woman with bleeding, as this can precipitate catastrophic hemorrhage if placenta previa or vasa previa is present 1, 5, 7
- Ultrasound may miss up to 50% of placental abruptions and 74% of ectopic pregnancies initially, requiring serial beta-hCG monitoring when initial imaging is non-diagnostic 1
- Normal vital signs do not exclude significant placental pathology, as placental abruption can present with normal hemodynamics initially but rapidly deteriorate 1
Long-Term Implications
First trimester bleeding, even when pregnancy continues, is associated with increased risk of preterm delivery, placental abruption later in pregnancy, and small for gestational age infants 1, 5