Yes, a face not visualized on the routine mid-trimester anomaly scan requires follow-up ultrasound imaging.
When one or more required fetal structures—including the face—are not adequately demonstrated during the anatomic examination, the patient should be brought back for a focused follow-up assessment 1. This is a clear recommendation from the 2021 ACR Appropriateness Criteria, which explicitly states that incomplete studies warrant repeat imaging.
Why Follow-Up Is Necessary
The face is a standard component of the mid-trimester anatomic survey, and facial anomalies (including cleft lip and palate) represent important congenital abnormalities that occur in the population 1. Missing this structure means the examination is incomplete by definition.
Timing and Approach
- Schedule the follow-up scan within 2-4 weeks of the initial examination, ideally before 22 weeks' gestation 2
- Use transabdominal ultrasound for focused assessment of the previously non-visualized structures 1
- Consider 3D/4D ultrasound if available, as these modalities have proven particularly helpful for evaluating facial anatomy, especially facial clefts 1
Clinical Context and Nuances
Completion Rates
Real-world data shows that even in optimal conditions (non-obese populations, skilled sonographers), approximately 4.2% of second-trimester scans remain incomplete due to unfavorable fetal position 3. The face specifically cannot be visualized in about 1.7% of cases on initial scanning 3. This is a technical limitation, not a reflection of sonographer skill.
Diagnostic Yield
While the incremental yield of repeat scanning decreases with each subsequent examination, research demonstrates that:
- 93.8% of anomalies are detected on the first scan
- 5.9% are detected on the second scan
- Only 0.3% require a third scan 4
The number of scans needed to detect one anomaly increases from 39 (first scan) to 189 (second scan) 4. However, this does not negate the clinical necessity of completing the anatomic survey when structures remain unvisualized.
Important Caveats
Do not confuse an incomplete scan with a low-yield screening scenario. The guidelines are clear: if required structures are not seen, follow-up is indicated regardless of statistical yield considerations 1. The goal is completion of the standard anatomic survey, not risk stratification.
Maternal body habitus matters. In obese patients, consider scheduling the follow-up scan at 20-22 weeks (about 2 weeks later than standard timing), and if still incomplete, repeat again in 2-4 weeks 1. Transvaginal ultrasound may supplement transabdominal imaging when fetal parts are close to the cervix 1.
When to Consider Advanced Imaging
If the face remains inadequately visualized after repeat standard ultrasound, or if an anomaly is suspected but incompletely characterized, fetal MRI may be indicated 1. MRI is particularly useful for evaluating cranial, facial, thoracic, abdominal, and pelvic anomalies, ideally performed at or after 22 weeks' gestation 1.
The International Society of Ultrasound in Obstetrics and Gynecology recommends fetal MRI when ultrasound information about an abnormality is incomplete, as it may confirm or complement findings and alter patient management 1.