What is the initial workup for a 16-week pregnant patient presenting to the emergency department with severe abdominal pain?

Emergency Department Workup for Severe Abdominal Pain in a 16-Week Pregnant Patient

A comprehensive ultrasound evaluation is essential for any pregnant patient at 16 weeks presenting with severe abdominal pain, regardless of vital sign stability, to rule out potentially life-threatening conditions. 1

Initial Assessment

Vital Signs and Physical Examination

• Complete vital sign assessment (blood pressure, heart rate, respiratory rate, temperature, oxygen saturation)
• Focused abdominal examination:
  • Location, character, and radiation of pain
  • Presence of rebound tenderness or guarding
  • Assessment for peritoneal signs
  • Uterine tenderness or contractions
• Pelvic examination:
  • Cervical status (dilation, effacement)
  • Vaginal bleeding or discharge
  • Adnexal tenderness or masses

Laboratory Studies

• Complete blood count with differential
• Comprehensive metabolic panel
• Urinalysis and urine culture
• Serum beta-hCG level
• Blood type and Rh status
• Coagulation studies
• Serum lipase and amylase (to rule out pancreatitis)

Imaging Studies

Ultrasound Evaluation

Ultrasound is the first-line imaging modality for pregnant patients with abdominal pain:

1. Obstetric ultrasound:

   • Confirm fetal viability
   • Assess placental location and integrity
   • Evaluate amniotic fluid volume
   • Check for signs of placental abruption

2. Abdominal/pelvic ultrasound:

   • Evaluate for appendicitis
   • Assess for gallbladder disease
   • Look for adnexal masses or ovarian torsion
   • Check for hydronephrosis or kidney stones
   • Evaluate for free fluid in the abdomen

The American College of Emergency Physicians guidelines emphasize that ultrasound should be performed regardless of beta-hCG levels in symptomatic pregnant patients 1. While ultrasound may have limitations (sensitivity of 0% for appendicitis in one study), it remains the initial imaging modality of choice due to safety in pregnancy 2.

MRI Consideration

If ultrasound is inconclusive and there is high clinical suspicion for surgical pathology:

• MRI should be considered as it has superior diagnostic capability for ruling out serious pathology 2
• Particularly useful for evaluating appendicitis, which ultrasound may miss in pregnancy

Differential Diagnosis to Consider

Obstetric Causes

• Ectopic pregnancy (though less likely at 16 weeks)
• Placental abruption
• Preterm labor
• Round ligament pain
• Uterine rupture (rare but life-threatening)

Non-Obstetric Causes

• Appendicitis (location may be altered due to gravid uterus)
• Cholecystitis/biliary colic
• Ovarian torsion
• Urinary tract infection/pyelonephritis
• Nephrolithiasis
• Pancreatitis (often misdiagnosed in pregnancy) 3
• Bowel obstruction
• Inflammatory bowel disease
• Herpes zoster (can present as severe localized pain before vesicle eruption) 4

Pitfalls and Considerations

1. Anatomical changes in pregnancy: The gravid uterus displaces abdominal organs, altering the typical presentation of conditions like appendicitis.

2. Misdiagnosis risk: Conditions like pancreatitis and shingles can be misdiagnosed in pregnancy, leading to inappropriate management 3, 4.

3. Delayed diagnosis: Pregnancy can mask symptoms of serious conditions, leading to delayed diagnosis and increased morbidity.

4. Radiation concerns: While ultrasound and MRI are preferred, necessary CT imaging should not be withheld if clinically indicated, as untreated surgical conditions pose greater risk.

5. Hydrosalpinx consideration: Though rare, hydrosalpinx can present as acute abdominal pain in pregnancy and should be included in the differential diagnosis 5.

Management Approach

1. Stabilize the patient: Ensure adequate IV access, fluid resuscitation if needed

2. Pain management: Acetaminophen is first-line; opioids may be considered for severe pain

3. Early consultation: Involve obstetrics early in the evaluation process

4. Surgical consultation: If appendicitis, cholecystitis, or other surgical pathology is suspected

5. Admission considerations: Low threshold for admission and observation if diagnosis remains unclear after initial workup

The emergency physician should maintain a high index of suspicion for both obstetric and non-obstetric causes of abdominal pain in pregnancy, as misdiagnosis can lead to significant maternal and fetal morbidity and mortality 6, 3.