Prenatal detection of preaxial upper limb reduction in trisomy 18.

BACKGROUND: Abnormalities of the upper and lower extremities, such as club feet, rocker-bottom feet, and abnormal hand posturing, are frequently detected prenatally in trisomy 18 fetuses. Aplasia of the radius, usually associated with the absence or hypoplasia of the first metacarpal and thumb, is the most prevalent reduction malformation in trisomy 18 infants. Because this anomaly is easily missed during prenatal ultrasonography, the role of prenatal detection of this particular preaxial upper limb reduction has not been emphasized. CASES: Three cases of trisomy 18 in which preaxial upper limb reduction (radial aplasia) was identified prenatally by ultrasound are reported. Although in all cases there were additional ultrasonographic findings suggestive of trisomy 18, the prenatal detection of preaxial upper limb reduction facilitated the diagnosis. CONCLUSION: Ultrasonographic examination of fetal forearms for the detection of preaxial upper limb reduction should be a routine part of the prenatal evaluation of fetuses in whom trisomy 18 is suspected.