FISH - Amnio one probe (Trisomy 21) / Down syndrome

FISH — Fluorescence In Situ Hybridization — looks directly at the chromosomes inside cells. This particular test examines cells from amniotic fluid (the fluid surrounding the baby) for one probe: chromosome 21. A third copy of chromosome 21 is what causes Down syndrome, hence the name trisomy 21.

Unlike the common screening tests (dual marker, NT scan) which only estimate risk, FISH works on the baby's own cells and gives a direct answer for chromosome 21 — usually faster than waiting for the full karyotype, which examines all chromosomes but takes longer.

When do doctors advise this test?

• A dual marker test or NT scan has shown increased risk for Down syndrome
• An ultrasound finding needs direct chromosomal confirmation
• Maternal age or family history puts the pregnancy at higher risk, as assessed by the obstetrician
• The doctor wants a rapid answer for chromosome 21 while the full karyotype is still in process

Preparation & the sample

No fasting is needed from the patient. The amniotic fluid sample is collected by your obstetrician through amniocentesis — a brief needle procedure usually done between the 15th and 20th week of pregnancy — at a clinic or hospital, not at our centre. Carry your doctor's referral and earlier screening reports (dual marker, NT scan) when the sample is submitted. Call +91 9451155402 to confirm how and where the specimen should reach the laboratory.

This information is educational and general. Your doctor's advice for your specific situation always comes first.