What is the most appropriate next diagnostic step to confirm fetal demise in an 18‑week pregnant woman presenting with decreased fetal movement and absent fetal heart tones?

Ultrasound Abdomen is the Next Diagnostic Step

The most appropriate next step is D. USG Abdomen (transabdominal ultrasound) to confirm fetal demise by documenting absent cardiac activity and to evaluate fetal anatomy, placental appearance, and amniotic fluid volume.

Diagnostic Approach for Suspected Fetal Demise at 18 Weeks

Primary Diagnostic Modality

• Transabdominal ultrasound is the gold standard for confirming fetal demise at 18 weeks gestation, as it can reliably document absent cardiac activity and assess fetal anatomy for structural abnormalities that may have caused the demise 1
• Real-time ultrasound visualization of the fetal heart is the most accurate method for diagnosing fetal death 2
• At 18 weeks, transabdominal imaging is sufficient for diagnosing pregnancy failure when an embryo's crown-rump length is >15 mm without visible cardiac activity 3

What the Ultrasound Should Assess

The comprehensive ultrasound examination should evaluate:

• Absence of cardiac activity (definitive confirmation of fetal demise) 1
• Fetal anatomy to identify any structural abnormalities that may explain the demise 1
• Placental appearance and location 1
• Amniotic fluid volume 1
• Signs of hydrops, growth restriction, or other pathology 1

Why Invasive Procedures Are NOT the Next Step

Timing of Invasive Testing

• Amniocentesis (Option A), placental tissue sampling (Option B), and umbilical cord sampling (Option C) should only be considered AFTER fetal demise is confirmed by ultrasound 1
• These invasive procedures are only indicated if there is a clinical need to determine the cause of death for counseling future pregnancies 1
• The Society for Maternal-Fetal Medicine recommends diagnostic testing including chromosomal microarray analysis when fetal growth restriction or malformations are detected, but this follows initial ultrasound diagnosis 1

Clinical Pitfall to Avoid

Never proceed directly to invasive testing without first confirming fetal demise with ultrasound. The clinical presentation (decreased fetal movement, absent fetal heart tones on examination) requires objective confirmation before any invasive procedures are considered 1, 2.

Management Implications After Diagnosis

Once fetal demise is confirmed by ultrasound:

• Active evacuation is recommended, not expectant management, due to increased risk of intrauterine infection, coagulopathy, and maternal sepsis with prolonged retention 1, 4
• At 18 weeks gestation, dilation and evacuation (D&E) is typically the preferred method 4
• All Rh-negative women must receive anti-D immunoglobulin to prevent alloimmunization 5, 4

Algorithm for This Clinical Scenario

1. Perform transabdominal ultrasound immediately to confirm absent cardiac activity
2. Document fetal measurements, anatomy, placental appearance, and amniotic fluid
3. Once fetal demise is confirmed, counsel regarding management options (surgical evacuation preferred at this gestational age)
4. Consider invasive testing (amniocentesis, tissue sampling) only if indicated for determining cause of death to guide future pregnancies
5. Administer Rh immunoglobulin if patient is Rh-negative

The answer is D. USG Abdomen - ultrasound confirmation must precede any consideration of invasive diagnostic procedures 1, 2.