What are the differential diagnoses for sharp right-sided pain in a woman who is 37 weeks pregnant?

Differential Diagnoses for Sharp Right-Sided Pain at 37 Weeks Pregnant

The most critical differential diagnoses to consider are appendicitis (the most common non-obstetric surgical emergency in pregnancy), followed by obstetric causes (placental abruption, preterm labor, HELLP syndrome), urolithiasis, ovarian torsion, and hepatobiliary pathology—all of which require urgent evaluation given the risk of maternal and fetal morbidity and mortality at this gestational age. 1

Surgical/Gastrointestinal Causes

Appendicitis

• Most frequently encountered non-obstetric surgical condition in pregnant women, occurring in approximately 1 in 20 women of childbearing age presenting with appendicitis 1
• Pregnant women are more likely to present with complicated (perforated or gangrenous) appendicitis, and perforation carries a higher risk of fetal loss, making early diagnosis critical 1
• At 37 weeks, the appendix is displaced superiorly and laterally by the gravid uterus, which can alter the typical presentation and location of pain 2
• Clinical outcomes are similar to non-pregnant women, though pregnant patients are more likely to undergo non-surgical management 1

Other Gastrointestinal Pathology

• Bowel obstruction or paralysis 2
• Inflammatory bowel disease (terminal ileitis) 1
• Endometriosis involving the appendix with serositis and perforation 2

Genitourinary Causes

Urolithiasis

• Urolithiasis can cause acute flank or right-sided pain in pregnancy, though the differential must account for physiologic hydronephrosis of pregnancy 1
• Physiologic hydronephrosis occurs in >80% of pregnant patients, more commonly on the right side, beginning in the second trimester 1
• Stones can cause obstruction superimposed on physiologic changes, requiring differentiation through imaging 1

Gynecologic/Obstetric Causes

Ovarian Torsion

• Ovarian torsion with necrosis is a critical diagnosis that can present with acute right-sided pain and requires urgent surgical intervention 2, 3
• May be associated with ovarian cysts or fallopian tube pathology 2
• MRI can identify adnexal masses or inflammation suggestive of torsion 3

Obstetric Emergencies (37 Weeks)

• Placental abruption: Sharp, constant pain with vaginal bleeding and uterine tenderness
• Preterm labor/contractions: At 37 weeks (early term), irregular contractions can cause sharp pain 2
• HELLP syndrome: Right upper quadrant/epigastric pain from hepatic involvement, but can radiate to right side
• Uterine rupture: Rare but catastrophic, presents with severe sharp pain and fetal distress

Other Gynecologic Causes

• Pelvic inflammatory disease or abscess 3
• Degenerating fibroid

Musculoskeletal/Inflammatory Causes

Infectious Sacroiliitis

• Rare but important differential presenting as severe pain in the right buttock radiating down the posterior thigh 4
• Associated with elevated WBC and CRP 4
• Requires MRI for diagnosis and should not delay medical treatment even in low-risk women 4

Round Ligament Pain

• Common benign cause, typically sharp and brief with movement
• Diagnosis of exclusion after ruling out serious pathology

Hepatobiliary Causes

• Acute cholecystitis/cholelithiasis: Right upper quadrant pain that may radiate to right side
• Hepatic pathology (less common but consider with HELLP syndrome)

Critical Diagnostic Approach

Initial Imaging Strategy

• Ultrasound should be the first-line imaging modality to determine if pathology is obstetric and assess fetal status 5
• If ultrasound is inconclusive, MRI abdomen/pelvis is the preferred next step at 37 weeks gestation 1, 3
• MRI has 96.8% sensitivity and 99.2% specificity for appendicitis in pregnancy, with excellent ability to identify alternative diagnoses including ovarian torsion and pelvic abscesses 1, 3
• CT should be reserved for situations where MRI is not immediately available or results remain inconclusive, using low-dose protocols when necessary 1

Key Clinical Features to Assess

• Fever and leukocytosis with neutrophil shift: Significantly higher in patients requiring surgery 5
• Gestational age correlation: Patients undergoing surgery had substantially higher gestational age 5
• Fetal status: Cardiotocography for fetal distress, which may indicate need for emergent cesarean section 2
• Radiation of pain: Buttock/posterior thigh radiation suggests sacroiliitis 4
• Associated symptoms: Vaginal bleeding, contractions, urinary symptoms, fever

Common Pitfalls

• Delayed diagnosis of appendicitis due to atypical location and presentation in late pregnancy can lead to perforation and fetal loss 1
• Assuming physiologic hydronephrosis without considering obstructing stone 1
• Overlooking ovarian torsion in the differential, which requires urgent surgical intervention 2, 3
• Relying solely on ultrasound in third trimester: Sensitivity for appendicitis is inversely correlated with gestational age 5