FISH-Prenatal Aneuploidy Detection (3 probes- Trisomy 18, X, Y) Test

The FISH-prenatal aneuploidy detection Test is a specialised genetic test performed on prenatal samples such as amniotic fluid or chorionic villus sampling (CVS). It uses fluorescent probes to check the number of specific chromosomes in foetal cells. This 3-probe version targets chromosomes 18, X, and Y to identify common chromosomal abnormalities.

Also known as Interphase FISH or Rapid Aneuploidy Screening (RAS), this test gives results faster than traditional karyotyping. Doctors typically recommend it when earlier screening tests or ultrasound findings suggest an elevated risk of chromosomal conditions.

The FISH-prenatal aneuploidy detection test is ordered when there is a clinical reason to check for specific chromosomal abnormalities in the foetus.

Common Symptoms That May Require This Test

A doctor may recommend this test based on one or more of the following clinical indications:

• Advanced maternal age (typically 35 years or older)
• Abnormal findings on an ultrasound scan
• Positive result from a first-trimester combined screening test or NIPT (non-invasive prenatal test)
• Increased nuchal translucency (extra fluid at the back of the baby's neck seen on scan)
• Previous pregnancy affected by a chromosomal abnormality
• Family history of chromosomal conditions
• Maternal preference for rapid results to reduce anxiety

Conditions This Test Can Help Detect

The 3-probe FISH-prenatal aneuploidy detection test can help identify the following chromosomal conditions:

• Trisomy 18 (Edwards syndrome): caused by an extra chromosome 18
• Turner syndrome (45, X): where a foetus has only one X chromosome instead of two
• Klinefelter syndrome (47, XXY): where a male foetus has an extra X chromosome
• Trisomy X (47, XXX): an extra X chromosome in female foetuses
• 47, XYY syndrome: an extra Y chromosome in male foetuses

The FISH-prenatal aneuploidy detection test procedure involves collecting a prenatal sample under medical supervision. Here is what you need to know before your appointment.

Do You Need to Fast?

No fasting is required for this test. You can eat and drink as normal before the procedure.

Practical Tips Before Your Test

Please keep the following points in mind before your appointment:

• Bring a detailed clinical history, including your symptoms, previous test results, and relevant scan reports, as this is required for the test
• Bring a duly signed PNDT Consent Form and Form-G, as required under PCPNDT guidelines
• In some cases, you may be advised to avoid using the toilet for a few hours before amniocentesis, as a full bladder can make the procedure easier
• Arrange for someone to drive you home after the procedure
• Inform your doctor if you are Rhesus negative, as an anti-D injection may be needed
• Tell your doctor about any medications you are taking

Step-by-Step Procedure

The sample collection method depends on whether amniotic fluid or CVS is being collected. Both procedures are performed by a trained medical specialist.

Amniocentesis (Amniotic Fluid Collection):

1. An ultrasound scan is performed so the doctor can see the baby throughout the procedure.
2. The skin over the abdomen is cleaned with an antiseptic solution.
3. A thin needle is carefully guided through the abdomen into the womb using the ultrasound image.
4. A small amount of amniotic fluid is drawn out and placed in a sterile container.
5. The sample is labelled and stored at the correct temperature before dispatch to the laboratory.
6. In the lab, fluorescent probes bind to specific chromosomes in the foetal cells, making them visible under a microscope for analysis.

Chorionic Villus Sampling (CVS):

1. An ultrasound scan is used to guide the procedure throughout.
2. A small sample of placental tissue (chorionic villi) is collected, either through the abdomen or through the cervix, depending on the position of the placenta.
3. The sample is placed in a sterile container and stored between 2°C and 8°C for transport.
4. In the laboratory, the chorionic villus sample is prepared, and fluorescent probes are applied to identify chromosome signals under a microscope.

Factors That Can Affect Accuracy

The following factors may affect the reliability of results:

• Maternal cell contamination in the sample (foetal cells mixed with mother's cells)
• Low levels of mosaicism (where only some foetal cells carry the chromosomal abnormality)
• Poor sample quality or insufficient cell count
• Gestational age below 15 weeks, when amniotic fluid samples may contain too few cells for reliable analysis

Chromosome number is determined at conception and is not influenced by diet or lifestyle. However, the following steps support a positive prenatal experience:

• Attend all scheduled prenatal appointments and follow your doctor's guidance throughout the pregnancy.
• Seek genetic counselling to fully understand your results and what they mean for your pregnancy.
• Maintain general prenatal wellness: balanced nutrition, adequate rest, and avoiding known environmental risks.

Follow these steps to book the FISH-prenatal aneuploidy detection test online at Lupin Diagnostics:

1. Select the test on the Lupin Diagnostics website.
2. Choose your city and preferred centre location.
3. Visit the centre at your scheduled time for sample collection.
4. Receive your report via email or WhatsApp within 3 days.