What is the next step for diagnosis in a patient at 18 weeks gestation with decreased fetal movement and no fetal heartbeat, despite previous normal findings?

Next Step for Diagnosis: Ultrasound Abdomen

The next step is ultrasound examination (Option D) to confirm fetal demise, assess fetal anatomy for structural abnormalities that may have caused the death, evaluate placental appearance, and measure amniotic fluid volume. 1

Diagnostic Approach at 18 Weeks with Absent Fetal Heartbeat

Immediate Confirmation with Ultrasound

• Ultrasound is the definitive diagnostic tool to document absent cardiac activity and confirm intrauterine fetal demise at 18 weeks gestation. 1

• The examination should assess for:

  • Absence of cardiac activity (definitive for fetal demise at this gestational age) 2, 1
  • Fetal anatomic abnormalities that may explain the demise 1, 3
  • Placental morphology and location 1
  • Amniotic fluid volume 1

• At 18 weeks, cardiac activity should be readily visible on ultrasound in a viable fetus, and its absence confirms demise. 2

Why Invasive Testing is NOT the Next Step

Amniocentesis (Option A), placental tissue sampling (Option B), and umbilical cord sampling (Option C) are NOT appropriate as the immediate next diagnostic step because:

• These invasive procedures are performed on living fetuses to obtain genetic material for karyotyping or to diagnose specific conditions. 2, 3

• With confirmed fetal demise, genetic testing can be performed after delivery through autopsy, placental examination, and tissue sampling, which is safer and more comprehensive. 3

• Invasive testing in the setting of fetal demise carries unnecessary maternal infection risk without providing immediate diagnostic benefit. 3

Subsequent Diagnostic Workup After Ultrasound Confirmation

Post-Delivery Evaluation

• A complete autopsy by a perinatal or pediatric pathologist should be strongly encouraged to determine the cause of fetal demise, provide prognostic information, and assess recurrence risk for future pregnancies. 3

• If complete autopsy is declined, at minimum obtain:

  • Partial or external autopsy 3
  • X-rays of the fetus 3
  • Photographs 3
  • Placental histopathology 3

• Genetic testing (karyotype or chromosomal microarray) can be performed on fetal tissue, placental tissue, or umbilical cord blood obtained at delivery. 2, 3

Maternal Evaluation

• Assess for maternal conditions that may have contributed to fetal demise, including:
  • Infection (TORCH titers, COVID-19 if applicable) 4
  • Thrombophilia screening 2
  • Diabetes and thyroid disorders 2
  • Hypertensive disorders 2

Common Pitfalls to Avoid

• Do not proceed directly to invasive testing (amniocentesis, chorionic villus sampling, or cordocentesis) without first confirming fetal demise with ultrasound, as this exposes the mother to unnecessary procedural risks. 3

• Do not delay ultrasound confirmation when fetal demise is suspected based on absent fetal heartbeat on Doppler, as timely diagnosis allows for appropriate counseling and management planning. 1

• Do not forgo autopsy and placental examination after delivery, as these provide critical information about the cause of death and recurrence risk that cannot be obtained through prenatal testing alone. 3