What could cause sharp left-sided rib pain that worsens on inhalation in a woman who is 15 weeks pregnant, and how should it be evaluated and managed?

Sharp Left-Sided Rib Pain During Inhalation at 15 Weeks Pregnancy

While pulmonary embolism must be ruled out given its status as a leading cause of maternal mortality, the most likely diagnosis in a 15-week pregnant woman with sharp left rib pain on inhalation is musculoskeletal—either costochondritis or a pregnancy-related rib stress injury from mechanical forces of the enlarging uterus.

Immediate Risk Stratification

The critical first step is determining whether this represents pulmonary embolism (PE), which accounts for 20% of maternal deaths in the United States 1. However, PE is confirmed in less than 10% of pregnant women presenting with concerning symptoms 1.

Red Flags Requiring Urgent PE Workup:

• Dyspnea (present in 62% of confirmed PE cases) 1
• Hypoxemia or oxygen saturation abnormalities
• Tachycardia
• Hemoptysis
• Syncope or unexplained hypotension
• Signs of deep venous thrombosis (leg swelling, pain, warmth)

If any red flags are present, proceed immediately with PE diagnostic algorithm below. If absent and pain is purely pleuritic/positional, musculoskeletal causes are more likely.

Diagnostic Algorithm for Suspected PE

If PE cannot be clinically excluded, follow this evidence-based approach 1:

Step 1: Assess for DVT Signs

• If leg symptoms present: Perform bilateral compression ultrasound (CUS) first

  • If positive → treat with anticoagulation
  • If negative → proceed to chest imaging 1

• If no leg symptoms: Skip CUS and go directly to pulmonary imaging 1

Step 2: Chest X-Ray (CXR)

Obtain CXR as the first radiation-associated test (strong recommendation) 1. This helps triage subsequent imaging and minimizes radiation exposure.

Step 3: Based on CXR Results

• Normal CXR: Proceed with V/Q lung scan (preferred over CT pulmonary angiography to minimize maternal breast radiation) 1, 2
• Abnormal CXR: Proceed with CT pulmonary angiography for better diagnostic yield 1

Important Caveat on D-Dimer:

Do not use D-dimer to exclude PE in pregnancy 1. Sensitivity is only 73% in pregnant women, with documented cases of PE despite negative D-dimer 1. This test is unreliable in pregnancy.

Musculoskeletal Causes (Most Likely at 15 Weeks)

If PE is ruled out or clinical suspicion is low, consider:

Pregnancy-Related Rib Stress Fracture

The enlarging uterus creates opposing muscular forces on the lower ribs, making them susceptible to stress fractures even with minimal trauma or chronic cough 3. This typically occurs in the third trimester but can present earlier 4.

Clinical features:

• Sharp, localized pain worsening with deep breathing, coughing, or movement
• Point tenderness over specific rib
• No systemic symptoms
• Pain reproduced by palpation

Management:

• Radiographic imaging is NOT necessary if clinical signs are obvious 4
• Adequate analgesia (acetaminophen first-line)
• Avoid NSAIDs after first trimester
• Reassurance that this resolves postpartum
• Consider regional anesthesia techniques (thoracic paravertebral block) for severe cases 5

Costochondritis

Inflammation of costochondral junctions, common in pregnancy due to chest wall expansion.

Management:

• Acetaminophen for pain control
• Reassurance
• Typically self-limited

Common Pitfalls to Avoid

1. Over-reliance on D-dimer: This test has poor specificity and inadequate sensitivity in pregnancy—do not use it 1

2. Delaying imaging due to radiation concerns: The radiation risk from appropriate diagnostic imaging is far lower than the mortality risk of missed PE. PE is a leading cause of maternal death 1

3. Assuming all chest pain is benign: While musculoskeletal causes are common, maintain high clinical suspicion for PE given its catastrophic consequences if missed

4. Ordering unnecessary imaging for obvious rib injury: If clinical examination clearly demonstrates localized rib tenderness without red flags, imaging adds no value and exposes the patient to unnecessary radiation 4

Bottom Line Approach

For this 15-week pregnant patient with isolated sharp left rib pain on inhalation:

1. Assess vital signs and oxygen saturation immediately
2. Ask specifically about: dyspnea at rest, leg swelling/pain, hemoptysis, syncope
3. If any red flags present: Follow PE algorithm starting with CXR 1
4. If no red flags and pain is reproducible on palpation: Diagnose musculoskeletal pain, provide acetaminophen, and reassure
5. Safety net: Instruct patient to return immediately if dyspnea, chest pain at rest, or leg swelling develops

The key is distinguishing between life-threatening PE (requires aggressive workup despite low yield) and benign musculoskeletal pain (requires only symptomatic management). When in doubt, err on the side of ruling out PE given its high maternal mortality 1.