Immediate Next Step: Ultrasound Abdomen (Option D)
The immediate next diagnostic step is ultrasound examination (USG Abdomen) 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
Rationale for Ultrasound as the Primary Diagnostic Tool
At 18 weeks gestation, ultrasound can reliably document absent cardiac activity and provide comprehensive assessment of the fetus and intrauterine environment. 1
The American College of Radiology recommends ultrasound-based assessments as the primary tools for evaluating fetal well-being in high-risk pregnancies, including situations of decreased fetal movement and suspected fetal demise. 2
Ultrasound allows immediate confirmation of fetal death without invasive procedures, which is the critical first step before considering any tissue sampling. 1
Why Invasive Testing (Options A, B, C) is NOT the Next Step
Timing and Sequence Issues
Invasive procedures like amniocentesis, placental tissue sampling, or umbilical cord sampling should only be considered AFTER fetal demise is confirmed by ultrasound and if there is a clinical indication to determine the cause of death. 3
The Society for Maternal-Fetal Medicine recommends that diagnostic testing including chromosomal microarray analysis be offered when fetal growth restriction or malformations are detected, but this follows initial ultrasound diagnosis, not precedes it. 3
Clinical Context
In cases of confirmed fetal demise at 18 weeks, the priority shifts to maternal safety and management of the demise, with tissue sampling considered only if there is specific indication for genetic or pathologic evaluation to guide future pregnancies. 1
Once fetal demise is confirmed, active evacuation is recommended due to increased risk of intrauterine infection, coagulopathy, and maternal sepsis with prolonged retention. 1
What the Ultrasound Should Evaluate
The comprehensive ultrasound examination should assess:
- Confirmation of absent cardiac activity (definitive diagnosis of fetal demise) 1
- Fetal biometry and anatomy to identify structural abnormalities that may explain the demise 1
- Placental appearance and location 1
- Amniotic fluid volume 1
- Any signs of hydrops, growth restriction, or other pathology 3
Important Clinical Caveat
Decreased fetal movement at 18 weeks is concerning but may be difficult for mothers to reliably assess at this early gestational age, as consistent fetal movement perception typically begins around 18-20 weeks. 4, 5 However, the absence of fetal heartbeat on current examination when it was previously present is the critical finding that mandates immediate ultrasound confirmation.