A 21-year-old female has sudden left lower quadrant pain and vaginal bleeding and denies pregnancy. Which diagnosis is most likely?

• A. Placenta previa.
• B. Abruptio placentae.
• C. Ruptured uterus.
• D. Ectopic pregnancy.

Answer: (D)

When reproductive-age patient presents with sudden unilateral lower quadrant pain and vaginal bleeding, pregnancy-related causes must be high on the differential. The most likely is an ectopic pregnancy, which occurs when a fertilized egg implants outside the uterine cavity, most commonly in the fallopian tube. This condition classically causes unilateral abdominal or pelvic pain with vaginal bleeding in early pregnancy. Even if the patient denies being pregnant, this presentation strongly points to a pregnancy complication because nonpregnancy causes of unilateral pain with vaginal bleeding are less likely to produce this exact combination.

Understanding why the other conditions fit less well helps solidify the choice. Placenta previa typically presents with painless vaginal bleeding later in pregnancy, not sudden abdominal pain. Abruptio placentae also involves painful bleeding but occurs in the later stages of pregnancy and often with a rigid, tender uterus and signs of fetal distress. A ruptured uterus is an acute, life-threatening event usually occurring during labor in someone with a known pregnancy history (e.g., prior cesarean or high-risk pregnancy) and presents with severe pain, signs of shock, and fetal compromise. These scenarios don’t align with a sudden unilateral pain and vaginal bleeding in an early-pregnancy context, making an ectopic pregnancy the best fit.