Ultrasound and Fetal Imaging
Core concepts
Know the components of the standard obstetric ultrasound at each trimester, including dating, anatomy survey, and growth assessment. Understand Doppler applications: umbilical artery, middle cerebral artery, ductus venosus, and uterine artery. Know the biometric parameters (BPD, HC, AC, FL) and their limitations in estimating fetal weight. Understand cervical length measurement technique and its role in preterm birth prediction. Know the ultrasound appearance of common anomalies and the significance of soft markers.
Understand fetal echocardiography indications and the four-chamber and outflow tract views. Know the role of MRI in evaluating fetal brain anomalies and the limitations of first-trimester imaging. Be familiar with 3D/4D applications and their limited diagnostic superiority over 2D in most settings.
Traps
- Relying on a single biometric parameter for growth assessment; use estimated fetal weight and growth velocity.
- Misinterpreting a short cervix as diagnostic of preterm birth without clinical context.
- Forgetting that soft markers are not diagnostic and should be interpreted with other risk factors.
- Assuming all Dopplers are equivalent; each vessel answers a different question.
- Overlooking that ultrasound dating is most accurate in the first trimester.
Rule of thumb
For any ultrasound finding, ask: what is the gestational age, what is the clinical context, and what is the next best test? A finding without context is not a diagnosis.
Worked example: A 32-week fetus has an estimated fetal weight below the 10th centile. Obtain umbilical artery Doppler; if the pulsatility index is elevated, this supports pathologic growth restriction and guides surveillance intensity.