Uterine Atony is the Most Likely Cause
In this patient with prolonged labor, chorioamnionitis, and oxytocin induction who develops postpartum hemorrhage, uterine atony (Option A) is the most likely cause. 1, 2, 3
Clinical Reasoning
Risk Factor Profile Strongly Favors Atony
This patient has multiple established risk factors that directly predispose to uterine atony:
Chorioamnionitis: This is a significant independent risk factor for postpartum hemorrhage, with an odds ratio of 6.45 (95% CI 2.37-17.64) for developing PPH. 3 Infection and inflammation impair myometrial contractility. 2
Prolonged labor with oxytocin augmentation: Induced or augmented labor is a well-established risk factor for uterine atony. 2 The prolonged exposure to oxytocin can lead to oxytocin receptor desensitization, resulting in poor uterine contractility after delivery. 2
Prolonged second stage: The patient labored for "several hours" before reaching 6 cm, then delivered 4 hours later, suggesting a prolonged labor course. Duration of second stage >2 hours is associated with prolonged third stage (HR 0.745,95% CI 0.628-0.883). 3
Epidemiologic Dominance of Atony
Uterine atony accounts for 70-80% of all postpartum hemorrhage cases and is the leading cause of early PPH. 1, 2, 4 This makes it statistically the most likely diagnosis in any case of postpartum bleeding unless specific findings point elsewhere. 1
Why Not the Other Options?
Placenta accreta (Option B) is unlikely because:
- The patient delivered vaginally without mention of difficulty with placental separation 1
- Accreta typically presents with inability to deliver the placenta or requires manual removal 1
- No risk factors mentioned (prior cesarean, placenta previa) 5
Cervical and vaginal lacerations (Options C & D) would be considerations if:
- The uterus were firm and well-contracted on examination 1
- The American College of Radiology specifically states that when the uterus is firm, genital tract trauma becomes the leading cause 1
- However, the question describes "large continuous vaginal bleeding" without mentioning uterine tone, and the clinical context (prolonged labor, infection, oxytocin use) overwhelmingly points to atony 1, 2
Clinical Approach
Immediate Assessment
- Assess uterine tone first: Palpate the fundus to determine if the uterus is soft and boggy (atony) versus firm and well-contracted (suggesting trauma). 1, 6
If Atony is Confirmed
- Uterine massage to stimulate contractions 6
- Administer additional uterotonics: Since she already received oxytocin for induction, add second-line agents early 2, 7
- Tranexamic acid 1 g IV over 10 minutes should be given immediately, as effectiveness declines by 10% for every 15 minutes of delay 8
Second-Line Uterotonic Agents
- Methylergonovine (contraindicated if hypertensive) 6
- Carboprost (15-methyl PGF2α) 2, 7
- Misoprostol (less effective than methylergonovine or carboprost but useful option) 2, 4
Critical Pitfall to Avoid
Do not delay treatment while waiting for the uterus to be examined. In the setting of this patient's risk factors (chorioamnionitis, prolonged labor, oxytocin augmentation), empiric treatment for atony should begin immediately while simultaneously assessing uterine tone and inspecting for lacerations. 1, 2 The combination of risk factors makes atony far more likely than traumatic causes, though both should be evaluated concurrently. 4