A 32-year-old multigravida at 30 weeks of gestation is admitted with regular uterine contractions every 5 minutes and cervical dilation of 3 cm. Vital signs are normal, and there is no vaginal bleeding. Speculum examination shows clear fluid in the vagina. What is the most common identifiable cause of preterm labor in this patient?

Explanation

## Epidemiology of Preterm Labor Causes **High-Yield:** PPROM is the *most common identifiable cause* of preterm labor, accounting for 25–35% of all preterm births. In this case, the clear fluid in the vagina (amniotic fluid) is the key diagnostic clue. ## Differential Diagnosis of Preterm Labor by Presentation | Cause | Frequency | Presentation | Key Diagnostic Sign | |-------|-----------|--------------|--------------------| | **PPROM** | 25–35% | Fluid leakage, regular contractions | Pooling of clear fluid on speculum | | **Idiopathic preterm labor** | 30–40% | Regular contractions, no identifiable cause | Normal membranes, no fluid leakage | | **Intrauterine infection** | 10–15% | Contractions, fever, maternal leukocytosis | Elevated inflammatory markers, positive cultures | | **Placental abruption** | 5–15% | Vaginal bleeding, uterine tenderness | Vaginal hemorrhage | | **Polyhydramnios** | 3–5% | Contractions, excessive amniotic fluid | Excessive AFI on ultrasound | ## Pathophysiology of PPROM-Induced Preterm Labor 1. **Rupture of fetal membranes** → loss of amniotic fluid barrier 2. **Ascending infection** (even subclinical) → bacterial colonization 3. **Inflammatory cascade** → IL-6, IL-8, TNF-α release 4. **Prostaglandin synthesis** → uterine contractions 5. **Preterm labor** ± delivery **Key Point:** PPROM can occur with or without clinical chorioamnionitis. Even "sterile" PPROM triggers an inflammatory response that initiates labor. ## Clinical Features Supporting PPROM in This Case - **Clear fluid in vagina** (amniotic fluid, not blood) - **Regular contractions** (prostaglandin-mediated) - **No vaginal bleeding** (excludes abruption) - **No fever or systemic signs** (infection may be subclinical) - **Multigravida** (higher risk for PPROM recurrence) **Clinical Pearl:** Speculum examination showing *pooling of clear fluid* is the gold standard for diagnosing PPROM. Avoid digital cervical examination until rupture is excluded, as it increases infection risk. **Mnemonic — PPROM Risk Factors: "INFECT"** - **I**nfection (UTI, STI, chorioamnionitis) - **N**utrition (low BMI, micronutrient deficiency) - **F**ibronectin (elevated fetal fibronectin at 16–24 weeks) - **E**thnicity (African descent higher risk) - **C**ervical insufficiency / cerclage - **T**rauma, tobacco, twin pregnancy [cite:Williams Obstetrics 25e Ch 34; ACOG Practice Bulletin #188]