August 2024
Ampath | ampath.co.za
Introduction
Non-invasive prenatal testing (NIPT) is a screening test that analyses cell-free DNA (cfDNA) from a maternal blood sample using next-generation sequencing (NGS).
What NIPT detects:
- Trisomies of chromosomes 21 (Down syndrome), 18, and 13
- Foetal gender
- Sex chromosome aneuploidies, including:
- Monosomy X
- Trisomy X
- XXY (Klinefelter)
- XYY
Optional Add-on:
- Analysis of all chromosomes (including segmental deletions/duplications >7Mb) is available with NIPT3
- This extended test requires upfront payment and pre-test genetic counselling
Platform used:
- VeriSeq™ NIPT Solution v2 (Illumina)
- CE-IVD approved
Eligibility Criteria
- Applicable from 10 weeks’ gestation onward
- Suitable for:
- Singleton pregnancies
- Twin pregnancies (only eligible for NIPT1)
- IVF pregnancies (self or donor eggs)
Not recommended for:
- Recent maternal blood transfusion
- Maternal malignancy
- Previous organ transplant
- Stem cell therapy
These conditions may cause false positives or false negatives.
NIPT Test Options
✅ NIPT1
- Chromosomes 21, 18, 13 ± Foetal gender
- Mnemonic:
NIPT1 - Cost (2024): R5,658.21
- Specimen: 1 x full Streck tube
- Turnaround time: 7 working days
✅ NIPT2
- Chromosomes 21, 18, 13 + Sex chromosome aneuploidies ± Foetal gender
- Mnemonic:
NIPT2 - Cost (2024): R6,344.01
✅ NIPT3
- All chromosomes ± Foetal gender
- Includes rare autosomal aneuploidies and CNVs >7Mb
- Mnemonic:
NIPT3 - Cost (2024): R9,425.00
- Requires pre-test counselling and upfront payment
Note: Testing for microdeletions is only performed on specific request and by arrangement.
Performance Metrics
(VeriSeq NIPT v2 data)
- Trisomy 21:
- Sensitivity: >99.9%
- Specificity: 99.9%
- Trisomy 18:
- Sensitivity: >99.9%
- Specificity: 99.9%
- Trisomy 13:
- Sensitivity: >99.9%
- Specificity: 99.9%
- Any anomaly (incl. sex chromosomes):
- Sensitivity: 95.5%
- Specificity: 99.3%
- Rare autosomal aneuploidies (RAA):
- Sensitivity: 96.4%
- Specificity: 99.8%
- Copy number variants (CNV >7Mb):
- Sensitivity: 74.1%
- Specificity: 99.8%
RAA and CNVs are only reported with NIPT3
Result Interpretation
✅ No Anomaly Detected
- Suggests low risk for the tested conditions
- Limitations:
- False negatives are possible
- Does not rule out other genetic or structural abnormalities
⚠️ Anomaly Detected
- Indicates high risk for a chromosomal abnormality
- Follow-up required: Diagnostic testing via CVS or amniocentesis
Possible causes of false positives include placental mosaicism or maternal chromosomal mosaicism.
Foetal Gender Reporting
- Result: Male or Female
- In twins:
- Y chromosome = at least one male
- No Y chromosome = both female
- Note: Gender determination may be inaccurate if the mother received a male organ transplant
📞 For more information, contact the NGS Laboratory:
Tel: 012 678 0645
Email: nipt@ampath.co.za
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