This involves genetic analysis of cells of fetal origin in various disorders by chorionic villus sampling, amniocentesis, or cord blood sampling, by karyotyping and FISH.
Indications:

• Women with advanced maternal age
• Previous child with a chromosome abnormality. 
• Women who have had previous still births or early neonatal deaths 
• Parents with balanced translocations 
• Cases in which the Triple Marker test of alpha fetoprotein, serum oestriol and beta HCG shows a high risk 
• Abnormalities seen on ultrasonography
  

The FISH technique is very useful for rapidly detecting aneuploidies in high-risk pregnancies. A ‘high risk’ for Trisomy 21 by the Triple test or Ultrasonography causes a lot of anxiety to the expectant couple, which can be relieved in a day by FISH on uncultured amniocytes. Karyotyping is simultaneously done to rule out other structural and numerical chromosome abnormalities. If the quantity of chorionic villi obtained in a biopsy is insufficient for karyotyping, FISH is still possible from interphase nuclei.
Sample:

• Amniotic fluid (8 ml for FISH; 15 ml for karyotyping; in 2-4 plain – red top – vaccutainers). In case of a sanguineous tap, collect in heparin vaccutainers.
• Cord blood (1ml in sodium heparin – green top – vaccutainer). 
• CVS in sterile normal saline with 2 drops of Gentamycin and sodium heparin or in media tubes supplied by the laboratory.