Factors influencing visualization of the intracranial translucency during first-trimester screening for aneuploidy.

OBJECTIVE

Neural tube defects occur in 1/2000 live births. Imaging of the intracranial translucency (IT) during first-trimester screening has been proposed as an early screen for open neural tube defects (ONTD). This study evaluates visualization of the IT and factors influencing its visualization during first-trimester ultrasound screening for aneuploidy.

METHODS

Ultrasound images for patients undergoing first-trimester screening for aneuploidy from January 1, 2009, through July 31, 2009, were reviewed for IT visualization, defined as an intracranial translucency parallel to the nuchal translucency. Second-trimester ultrasounds and delivery records were reviewed for the presence of fetal ONTD.

RESULTS

The IT was visualized in 74.8% of 759 gestations studied at a mean gestational age of 12 weeks, 5 days. Among gestations where the IT was visualized, we found a larger crown-rump length, lower maternal weight, and more fetuses in the supine position (p < 0.0001). Predictive models for visualization of the IT were formulated based on these factors.

CONCLUSION

The IT can be visualized in the majority of patients in the standard midsagittal plane used for measurement of the nuchal translucency. Visualization is significantly associated with crown-rump length, gestational age, maternal weight, and fetal position. Visualization of the IT is feasible.