Second-trimester ultrasonography: determinants of visualization of fetal anatomic structures

Little information has been published regarding rates of visualization of fetal anatomic structures or factors affecting visualization in unselected patients. We prospectively studied these points by scoring visualization of intracranial, spinal, cardiac, ventral wall, umbilical cord, stomach, bladder, and genital anatomy in 573 consecutive midtrimester scans in which no fetal anomalies were seen. Each feature was scored 0, 1, or 2, corresponding to poor, adequate, or optimal visualization, and these eight numbers were summed for an overall visualization score. Overall visualization fell abruptly beyond maternal weight 165 pounds (p less than 0.001) and rose with advancing gestational age (p less than 0.001). Placental location did not significantly influence visualization. Overall, an adequate screening scan, defined as adequate visualization of central nervous system, heart, stomach, ventral wall, bladder, and cord was obtained in 51% of scans, and optimal visualization of each of these in only 9% of cases. Factors that might improve anatomic visualization and the implications of these results for the use of ultrasonography in screening for congenital anomalies are discussed.