Prenatal detection of fetal trisomy 18 through abnormal sonographic features.

Objective: To describe the prenatal detection of fetal trisomy 18 through abnormal sonographic features and to determine the sensitivity of sonographically detecting fetuses with trisomy 18.

Methods: All genetic and cytogenetic records of fetuses with trisomy 18 were reviewed retrospectively (1992-2002). From these, singleton fetuses who had prenatal sonography at our unit were identified. The maximal numbers of individual abnormalities from 1 sonographic examination (not limited to type of organ system) were recorded. Each abnormality was classified as major, minor, or "other," and each organ system was classified as abnormal only once, regardless of the number of individual abnormalities identified in that system. The sensitivity of sonography in detecting abnormalities of trisomy 18 was determined.

Results: Of 38 fetuses identified with trisomy 18, all had 4 or more prenatally detected sonographic abnormalities (sensitivity of sonographic detection of fetuses with trisomy 18, 100%). The median number of abnormalities per examination was 8 (range, 4-19). Sonographically detected major abnormalities were cardiac (84%; n = 32), central nervous system (87%; n = 33), gastrointestinal (26%; n = 10), and genitourinary (16%; n = 6). Sonographically detected minor abnormalities were short ear length below the 10th percentile for gestational age (96%; n = 26/27), upper extremities and hands (95%; n = 36), lower extremities and feet (63%; n = 24), and face (53%; n = 20). Fifty percent (19 of 38) had choroid plexus cysts identified, but this was never an isolated finding.

Conclusions: In experienced hands, the sensitivity of detecting fetal trisomy 18 on prenatal sonography is 100%, and all cases will have multiple anomalies visualized.