- Advanced maternal age (≥35 years at EDD) - Abnormal ultrasound findings - Positive maternal serum screening - Previous history of chromosome abnormality - Family history of Down syndrome - Parental anxiety
Amniotic fluid (3ml), chorionic villi (5mg), or fetal cord blood/neonate blood (1.0ml)
FISH assay using LSI 13 and 21, and CEP X, Y, and 18 DNA probes labelled with fluorophores and analysed under fluorescence microscopy.
Normal or Abnormal. If Abnormal, the abnormality is described in accordance to the International System for Human Cytogenomic Nomenclature (ISCN, 2020).
Individuals with a trisomy will show three copies of a particular DNA probe. Normal individuals will show two copies of each DNA probe. Females will show two copies of the X probe, males one copy of the X and Y probe each.
1 ~ 3 days
Monday – Friday (office hours)
This FISH test is usually requested in conjunction with conventional cytogenetic studies.