Trisomy 21 and cystic hygromas in early gestational age fetuses.

Chromosomal aberrations are associated with 60% of cystic hygromas and the majority of these are females with a 45,X karyotype. Trisomy 21 has rarely been reported. Six cases of cystic hygromas with trisomy 21 were detected during a 6-month time period in our laboratory. An earlier gestational age of 14 weeks was present in our cases compared with a gestational age of 18 weeks reported in the literature. Because of the high rate of fetal loss prior to 16 weeks, many cases of trisomy 21 with cystic hygromas may go undetected. This suggests that cystic hygromas detected before 16 weeks of gestation may be clinically different from those detected later in gestation. With the increasing use of chorionic villus sampling and amniocentesis at 10 to 12 weeks of gestation, trisomy 21 may be a common finding in fetuses with cystic hygromas.