44-50% of Edwards syndrome (trisomy 18) cases will present with CPC, and 1.4%
of Down syndrome (trisomy 21) cases will present with CPC. ~75%
of abnormal karyotypes (obtained by chorionic villus sampling or amniocentesis) associated with CPCs are trisomy 18, while the remainder are trisomy 21.[2]
CPCs typically disappear later during pregnancy, and are considered soft markers. They are usually harmless, and studies have shown that they have no effect on infant and early childhood development.