A 24-year-old multigravida at 30 weeks gestation with a history of recurrent preterm labor is counseled about the difference between threatened preterm labor and preterm premature rupture of membranes (PPROM). Which finding is the best discriminator between these two conditions?

## Distinguishing Threatened Preterm Labor from PPROM ### Key Discriminating Feature **Key Point:** Rupture of the amniotic membrane (demonstrated by positive fern test, pooling of fluid, or nitrazine positivity) is the defining pathology of PPROM and is absent in threatened preterm labor. ### Comparative Clinical Features | Feature | Threatened Preterm Labor | PPROM | |---------|------------------------|-------| | **Uterine contractions** | Present, regular, ≥2/10 min | May be absent initially | | **Cervical dilation** | Progressive (≥80% effaced or ≥2 cm dilated) | Variable; may be minimal | | **Amniotic membrane integrity** | Intact | Ruptured (diagnostic) | | **Fern test** | Negative | Positive (crystallization pattern) | | **Pooling of fluid** | Absent | Present on speculum exam | | **Nitrazine paper** | Negative (pH <6.0) | Positive (pH >6.0, blue-green) | | **Vaginal discharge** | Mucoid, scanty | Copious, watery, clear | | **Risk of infection** | Lower | Higher (chorioamnionitis risk) | ### Why This Matters **Clinical Pearl:** PPROM is diagnosed clinically — the patient reports a gush or continuous leakage of fluid, and the diagnosis is confirmed on speculum exam (not digital cervical exam, which increases infection risk). Threatened preterm labor is diagnosed by contractions + cervical change with intact membranes. **High-Yield:** The fern test is the most sensitive bedside test for PPROM. A positive fern (ferning pattern under microscopy) indicates amniotic fluid and confirms membrane rupture. Pooling of fluid in the posterior vaginal fornix on speculum exam is equally diagnostic. **Warning:** Do NOT perform digital cervical examination in suspected PPROM until rupture is excluded — digital exam increases the risk of ascending infection and chorioamnionitis. ### Mnemonic: PPROM vs LABOR - **PPROM** = **P**ooling + **P**ositive fern + **P**remature rupture - **Labor** = **L**ower segment changes + **L**ower segment contractions + **L**ower risk of infection [cite:Williams Obstetrics 26e Ch 34]