other diagnostic techniques such as immunocytochemistry (icc) evaluation are usually followed by fish or polymerase chain reaction to detect chromosomal aneuploidies. maternal blood sampling for fetal cells, often used to identify risk of trisomies 18 or 21, poses less risk as compared to amniocentesis and chorionic villous sampling (cvs). chorionic villus sampling utilizes placental tissue to give information about fetal chromosome status and has been used since the 1970s. in addition to cvs, amniocentesis can be used to obtain fetal karyotype by examining fetal cells in amniotic fluid. it was first performed in 1952 and became standard practice in the 1970s. the odds of having a child with polysomy increases as the age of the mother increases, so pregnant women over the age of 35 are tested. restriction fragment length polymorphism (rflp) analysis rflps can be used to determine the origin and mechanism involved with polysomy x and other chromosome heteromorphisms or chromosomes that differ in size, shape, or staining properties. restriction enzymes cut dna at a specific site and the dna fragments that are left are called restriction fragment length polymorphisms, or rflps. rflp also aids in the identification of the huntingtin (htt) gene which is predictive of an adult-onset autosomal disorder called huntington's disease (hd). mutations in chromosome 4 are able to be visualized when rflp is used in conjunction with southern blot analysis. flow cytometry human lymphocyte cultures may be analyzed by flow cytometry to assess chromosomal abnormalities, such as polyploidy, hypodiploidy, and hyperdiploidy. flow cytometers have the ability to analyze thousands of cells each second and are commonly used to isolate specific cell populations.