Abruptio Placentae (Placental Abruption)
The most likely diagnosis is abruptio placentae (placental abruption), given the classic triad of sudden-onset abdominal pain, vaginal spotting (often dark blood), and a firm, tender uterus in a term pregnancy. 1
Clinical Reasoning for This Diagnosis
The presentation is pathognomonic for placental abruption based on several key features:
Painful vaginal bleeding is the hallmark distinguishing feature—placental abruption typically presents with abdominal pain, whereas placenta previa characteristically presents with painless bleeding 2
Firm, tender uterus on palpation indicates concealed hemorrhage at the decidual-placental interface with uterine irritability, which is diagnostic of abruption 1
Tachycardia (pulse 118) with relatively normal blood pressure suggests early compensated shock from ongoing hemorrhage 1
Sudden onset at 37 weeks is consistent with the acute nature of placental separation 1
Why Other Diagnoses Are Excluded
Placenta Previa (Option C)
- Placenta previa presents with painless vaginal bleeding, not the painful presentation described here 2
- The uterus would be soft and non-tender, not firm and tender 3
- While placenta previa affects approximately 1 in 200 pregnancies, the painful presentation rules this out 2
Uterine Rupture (Option D)
- Uterine rupture is exceedingly rare in a primigravida (first pregnancy) with no history of prior cesarean delivery or uterine surgery 2
- Would typically present with more severe hemodynamic instability and loss of fetal station 2
Endometritis (Option B)
- Endometritis occurs postpartum, not during pregnancy 1
- Would present with fever and purulent discharge, neither of which are present (temperature is normal at 37.0°C) 1
Critical Management Implications
Placental abruption is a true obstetric emergency requiring immediate intervention:
Restoration of circulating volume is the first priority, followed by expeditious delivery (typically cesarean section for a viable fetus at 37 weeks) 1
The firm, tender uterus indicates significant hemorrhage at the decidual-placental interface, which can rapidly progress to maternal shock, disseminated intravascular coagulopathy, and fetal death 1
Ultrasound may be performed but is insensitive—detecting at most 50% of abruption cases—so the diagnosis is primarily clinical based on the presentation described 2, 1
Do not delay delivery for imaging when clinical presentation is this clear, as severe abruption significantly impacts fetal and maternal morbidity and mortality 1
Common Pitfall to Avoid
The most dangerous error would be attributing this to normal labor or dismissing the severity based on relatively stable vital signs—the tachycardia indicates ongoing blood loss, and placental abruption can deteriorate rapidly from compensated to decompensated shock 1