What is the appropriate management for a 6-month pregnant woman presenting with abdominal pain?

Management of Abdominal Pain in a 6-Month Pregnant Woman

Ultrasound should be the initial imaging modality for evaluating abdominal pain in a pregnant woman at 6 months gestation, followed by MRI without contrast if ultrasound is inconclusive or non-diagnostic, while avoiding CT unless the clinical scenario is life-threatening and MRI is unavailable. 1, 2

Initial Clinical Assessment

Critical Red Flags to Identify Immediately

• Hemodynamic instability (hypotension, tachycardia, signs of shock) requires immediate resuscitation and urgent intervention 1, 2
• Fever with tachycardia and tachypnea suggests serious intra-abdominal infection requiring emergent evaluation 1, 2
• Vaginal bleeding with abdominal pain raises concern for placental abnormalities or obstetric complications 2
• Severe localized pain with peritoneal signs may indicate surgical emergency such as appendicitis or bowel perforation 1, 2

Key History Elements

• Pain characteristics: Location (noting that normal anatomical landmarks are displaced by the gravid uterus), onset, severity, radiation 1, 3
• Associated symptoms: Vaginal bleeding, fever, nausea/vomiting, urinary symptoms, changes in fetal movement 2, 4
• Obstetric history: Gestational age confirmation, pregnancy complications, prior cesarean sections 4, 3
• Surgical history: Previous bariatric surgery (internal herniation can be fatal if treatment delayed >48 hours) 2

Physical Examination Pitfalls

• Pain location may not correlate with underlying pathology due to anatomical displacement by the enlarged uterus 1, 2
• Appendicitis pain may not localize to the right lower quadrant as expected in non-pregnant patients 1, 2
• Peritoneal signs may be less pronounced or absent despite serious pathology 4, 3

Differential Diagnosis by Category

Obstetric Causes (Most Common at 6 Months)

• Placental abnormalities including abruption 2
• Preterm labor 4, 3
• Uterine stretching and round ligament pain (typically mild and self-limited) 2

Non-Obstetric Surgical Emergencies

• Appendicitis is the most common cause requiring emergency surgery in pregnancy 1, 2
• Cholecystitis and biliary colic 1, 2
• Bowel obstruction (higher risk if prior abdominal surgery) 3, 5
• Ovarian torsion (less common at 6 months but still possible) 1, 2
• Internal herniation (critical in post-bariatric surgery patients) 2

Medical Causes

• Urinary tract infection and pyelonephritis 1, 2
• Nephrolithiasis 1, 2
• Pancreatitis 1, 2
• Inflammatory bowel disease flare 1, 2

Diagnostic Imaging Algorithm

Step 1: Ultrasound as Primary Modality

• Perform ultrasound first for all pregnant patients with abdominal pain regardless of clinical suspicion 1, 2
• Ultrasound can diagnose: cholecystitis, hydronephrosis, ovarian masses, free fluid, and sometimes appendicitis 1
• Do not skip ultrasound even if clinical suspicion is high for conditions traditionally diagnosed by CT 1

Step 2: MRI When Ultrasound is Non-Diagnostic

• MRI without contrast is the next step when ultrasound findings are equivocal or non-diagnostic 1, 2
• MRI has 94% sensitivity and 96% specificity for appendicitis 1
• Modern protocols can be completed in under 10 minutes 1
• MRI can be performed without contrast and still provide diagnostic information, avoiding gadolinium exposure 1
• MRI effectively evaluates: appendicitis, bowel obstruction, pancreatitis, hepatobiliary disease, and renal pathology 5, 6

Step 3: CT Only in Life-Threatening Scenarios

• Reserve CT for emergent situations where MRI is unavailable and immediate diagnosis is critical for maternal survival 1
• The risk of radiation to the fetus must be weighed against the risk of delayed diagnosis in a life-threatening condition 1

Laboratory Evaluation

Essential Initial Labs

• Complete blood count to assess for leukocytosis (though pregnancy normally elevates WBC) and anemia 1, 2
• Urinalysis and urine culture (UTI is common in pregnancy) 2
• Liver function tests if right upper quadrant pain or concern for hepatobiliary disease 1
• Lipase if epigastric pain or concern for pancreatitis 1
• Lactate if concern for bowel ischemia or sepsis 1

Interpretation Caveats

• Mild leukocytosis (up to 15,000) is normal in pregnancy 4, 3
• Physiologic changes of pregnancy alter many laboratory reference ranges 4, 3

Management Principles

When Surgical Intervention is Indicated

• Do not delay necessary surgery due to pregnancy; maternal mortality from delayed treatment of surgical emergencies far exceeds risks of anesthesia and surgery to the fetus 3, 5
• Laparoscopic approaches are safe and preferred when feasible 1, 3
• Appendicitis requires prompt surgical intervention regardless of gestational age 2, 3

Conservative Management Considerations

• Mild, non-specific pain without red flags can be managed conservatively with close follow-up 2
• Avoid NSAIDs including indomethacin in pregnancy, particularly after 20 weeks, due to risk of premature ductus arteriosus closure, oligohydramnios, and renal dysfunction 7
• Acetaminophen is the preferred analgesic in pregnancy 8

Obstetric Consultation

• Involve obstetrics early for all pregnant patients with acute abdominal pain 4, 3
• Fetal monitoring should be initiated if gestational age is viable (typically ≥24 weeks) 3

Common Pitfalls to Avoid

• Attributing all abdominal pain to normal pregnancy changes without adequate evaluation 4, 3
• Delaying imaging due to radiation concerns when ultrasound and MRI are radiation-free alternatives 1, 6
• Assuming typical pain patterns when anatomical displacement alters presentation 1, 2
• Failing to consider surgical emergencies that require prompt intervention regardless of pregnancy 3, 5
• Using discriminatory β-hCG thresholds to defer ultrasound in early pregnancy (though less relevant at 6 months) 1