What information on fetal anatomy can be provided by a single first-trimester transabdominal three-dimensional sweep?

To determine the extent to which the fetal anatomy detailed in The Fetal Medicine Foundation Nuchal Translucency software program can be visualized using the stored dataset of a single transabdominal three-dimensional (3D) volume sweep of the entire fetus between 11 and 13 + 6 weeks' gestation.

Transabdominal 3D volume sweeps of the entire fetus in 273 singleton pregnancies were performed in the mid-sagittal plane (Observer 1). The datasets were copied to a compact disc and manipulated on a personal computer using ultrasound software in the sectional planes mode. Each dataset was manipulated and analyzed by two separate investigators (Observers 2 and 3), who were blinded to each other's results.

The crown-rump length (CRL) and nuchal translucency thickness (NT) were measured by both investigators in 100% and 84.6% of cases, respectively. Increasing maternal weight significantly reduced the odds of the investigators being able to visualize most of the anatomical characteristics tested, and increasing CRL significantly increased the odds of the investigators being able to identify half of the characteristics tested. There were negligible clinical differences in measurements of NT and CRL between the three observers. Paired t-tests and intraclass correlations showed that, while there were statistically significant differences for NT measurements, the effect size was small and would have little clinical impact on screening results.

A single transabdominal 3D sweep at 11 to 13 + 6 weeks' gestation provides appropriate views of the fetus for evaluation of both anatomy and NT in the vast majority of cases.