What is a potential cause of uterine atony?

Distended Bladder is a Potential Cause of Uterine Atony

A distended bladder is a potential cause of uterine atony, as it can mechanically interfere with proper uterine contraction after delivery. Among the options presented (distended bladder, Von Willebrand disease, preterm delivery, and preeclampsia), only a distended bladder directly contributes to uterine atony by preventing effective contraction of the uterine muscle.

Understanding Uterine Atony

Uterine atony is characterized by the failure of the uterus to contract effectively after delivery, which is the most common cause of postpartum hemorrhage (PPH), accounting for more than 75% of early PPH cases 1. When the uterus fails to contract properly:

• The uterus is palpable above the umbilicus because the relaxed, non-contracted uterine muscle fails to compress blood vessels at the placental site
• This leads to significant blood accumulation within the uterine cavity
• The uterus becomes enlarged and displaced upward 1

Analysis of the Options

Distended Bladder

• A distended bladder can physically interfere with uterine contraction by:
  • Occupying space in the pelvis that prevents the uterus from contracting effectively
  • Mechanically displacing the uterus and disrupting normal contractile function
  • Creating pressure against the uterine wall that inhibits proper muscle contraction

Von Willebrand Disease

• Von Willebrand disease is a bleeding disorder that affects blood clotting
• While it can contribute to postpartum hemorrhage due to coagulopathy, it does not directly cause uterine atony
• Coagulopathy is mentioned as a separate cause of PPH distinct from uterine atony 2

Preterm Delivery

• Preterm delivery is not specifically identified as a direct cause of uterine atony in the evidence provided
• While complications may occur with preterm deliveries, the uterine muscle's ability to contract is not inherently impaired by gestational age alone

Preeclampsia

• Preeclampsia is mentioned as a potential risk factor for PPH through coagulopathy mechanisms 2
• However, it is not directly identified as a cause of uterine atony itself
• The evidence indicates that severe pre-eclampsia is associated with coagulopathy rather than primary uterine muscle dysfunction 2

Risk Factors for Uterine Atony

According to the evidence, other risk factors for uterine atony include:

• Induced or augmented labor
• Chorioamnionitis
• Obesity
• Multiple gestation
• Polyhydramnios
• Prolonged second stage of labor 3

Clinical Diagnosis of Uterine Atony

Uterine atony is primarily diagnosed clinically by:

• Palpable uterine fundus above the umbilical level
• Soft and boggy uterus on palpation
• Excessive vaginal bleeding
• Vital sign changes consistent with blood loss (tachycardia, hypotension) 1

Management Considerations

When uterine atony is suspected, management includes:

1. Identifying and addressing contributing factors (such as emptying a distended bladder)
2. Uterine massage
3. Administration of uterotonic drugs:
   • Oxytocin (first-line agent) 4, 5, 6
   • Methylergonovine or carboprost (second-line agents) 4, 5, 6

Conclusion

Among the options presented, a distended bladder is the correct answer as a potential cause of uterine atony. It directly interferes with the uterus's ability to contract effectively after delivery, while the other options (Von Willebrand disease, preterm delivery, and preeclampsia) are not directly linked to uterine muscle dysfunction in the evidence provided.