Previa versus abruption, and why one exam is forbidden
PREVIA VERSUS ABRUPTION
Both present as bleeding after twenty weeks. The distinction is anatomic, and every other difference follows from the anatomy. Previa is a placenta lying over or near the internal cervical os. Abruption is a normally implanted placenta separating from the decidua before birth.
| PLACENTA PREVIA | ABRUPTIO PLACENTAE | |
|---|---|---|
| Anatomy | Placental tissue over or near the internal cervical os. Current usage describes complete previa when the os is covered and low-lying placenta when the edge sits near but not over the os; the older partial and marginal subdivisions have been consolidated | Premature separation of a normally implanted placenta from the uterine decidua, partial or complete |
| Bleeding | Painless, bright red, external. Often recurrent and self-limited at first, then heavier with each episode | May be dark red. May be concealed behind the placenta, so what is seen can badly understate what is lost |
| Pain and uterine tone | Uterus soft and nontender; normal tone between contractions | Sudden onset of pain, uterine tenderness, a rigid or board-like abdomen, frequent low-amplitude contractions, rising resting tone |
| Fetal status | Often reassuring early, because the exchange surface is intact until bleeding is significant | Exchange surface is lost, so late decelerations, minimal or absent variability, and bradycardia appear early |
| Risk context | Prior cesarean or other uterine surgery, prior previa, multiparity, multiple gestation, advanced maternal age, smoking | Hypertensive disorders, trauma including motor vehicle collision and intimate partner violence, cocaine use, prior abruption, sudden uterine decompression, smoking |
| Nursing actions | No digital and no speculum cervical examination. Continuous fetal and uterine monitoring, large-bore intravenous access, type and screen, bed rest and pelvic rest as ordered, plan for cesarean birth if the os is covered | Continuous monitoring, large-bore access, volume resuscitation, evaluate for disseminated intravascular coagulation, anticipate expedited birth |
SHARED RULE
Any vaginal bleeding after twenty weeks is evaluated, and placental location is confirmed by ultrasound, before any cervical examination is performed. A digital examination in the presence of a previa can perforate the placenta and cause catastrophic hemorrhage in seconds. This is an absolute boundary, not a preference.
Watch outin abruption, concealed bleeding hides the real loss. Rising fundal height, a firming uterus, and maternal tachycardia with a falling blood pressure can be the only external evidence that liters are already gone.
Margin notepainless equals previa. Painful and rigid equals abruption. Hemorrhage response → BOOK 12 · P9. Coagulation values → BOOK 07 · P4. Shock classification → BOOK 09 · P7
Takeawaypain and uterine rigidity separate the two faster than the bleeding does, and suspected previa forbids the digital exam.