Choroid plexus cysts and chromosomal defects During a 4-year period, 83 pregnant women with fetal choroid plexus cysts were investigated in our unit. Abnormal karyotypes were found in 20 fetuses, including trisomy 18 (n = 16), trisomy 13 (n = 1), triploidy (n = 1) and translocation Down's syndrome (n = 2). All fetuses with chromosomal defects had structural malformations in addition to the choroid plexus cysts. 