Non-invasive prenatal testing (NIPT), also called cell-free DNA screening, analyses small fragments of placental DNA that circulate in the mother’s blood. From 10 weeks, a single blood sample can screen for Down syndrome (trisomy 21), Edwards syndrome (trisomy 18) and Patau syndrome (trisomy 13), with a higher detection rate and far fewer false alarms than the older blood tests.
NIPT is still a screening test. A higher-chance result must be confirmed with a diagnostic test before any decision is made, and a low-chance result does not rule out every condition. Understanding these limits before the blood is taken is exactly what genetic counselling is for.
At Divine Women’s Hospital, Gota, Dr. Devang Patel offers counselling before and after NIPT and other genetic tests, alongside the NT and anomaly scans, so the blood test and the ultrasound findings are interpreted together. Counselling is available in Gujarati, Hindi and English.
How NIPT works
During pregnancy, cells from the placenta release small pieces of DNA into the mother’s bloodstream. In a typical sample at 10 to 12 weeks, around 10% of the free DNA (the fetal fraction) comes from the placenta. The laboratory counts DNA pieces from each chromosome; an excess from chromosome 21, for example, suggests trisomy 21.
Because the DNA comes from the placenta rather than the baby directly, results occasionally differ from the baby’s true chromosomes. This is called confined placental mosaicism, and it is one of the reasons a higher-chance result is always confirmed, usually by amniocentesis rather than CVS, which samples the placenta itself.
Other factors can affect the result: a vanishing twin, a maternal chromosomal variation, a recent blood transfusion, organ transplant or, rarely, a cancer in the mother. Your history is checked for these before the sample is taken. The fetal fraction is lower with higher body weight and very early testing, which is why 10 weeks is the earliest recommended point.
What NIPT can and cannot tell you
- Trisomy 21: detection about 99%, false-positive rate about 0.1% in published studies
- Trisomy 18 (about 97%) and trisomy 13 (about 90%) have slightly lower detection
- Sex chromosome differences are not reported in India because of the PCPNDT Act
- Microdeletions and genome-wide panels have lower accuracy and more false positives, and are discussed individually
- It does not check the baby’s anatomy, heart, placenta or pre-eclampsia risk
- It does not diagnose: a higher-chance result is confirmed by CVS or amniocentesis
Comparing your screening and testing options
Couples often ask which test to choose. The table compares the main options; many pregnancies combine the NT scan with either the double marker or NIPT.
| Test | When | What it offers |
|---|---|---|
| Combined test (NT + double marker) | 11–13+6 weeks | About 90% detection for Down syndrome, early anatomy, pre-eclampsia screening |
| NIPT | From 10 weeks | About 99% detection for Down syndrome, very few false positives; no anatomy |
| Quadruple test | 15–20 weeks | About 75–80% detection; for those who missed first-trimester screening |
| CVS (diagnostic) | 11–14 weeks | Definite chromosomal or genetic answer; small procedure-related miscarriage risk |
| Amniocentesis (diagnostic) | From 15 weeks | Definite answer; procedure-related miscarriage risk well under 1 in 200 |
Positive predictive value: why a higher-chance result is not a diagnosis
Accuracy depends on how common the condition is in your situation. For a 25-year-old, a higher-chance result for trisomy 21 is correct in roughly 50 to 80% of cases; for a 40-year-old, closer to 95%. For trisomy 13 and for microdeletions, many higher-chance results are false.
That is why no decision about the pregnancy should ever be made on NIPT alone. A diagnostic test, usually amniocentesis from 15 weeks, confirms or excludes the result.
A low-chance result is very reliable for trisomy 21: fewer than 1 in 10,000 low-chance results are missed cases in most published series. It allows most couples to avoid an invasive test altogether.
NIPT tells you whether to test further. Only CVS or amniocentesis gives a diagnosis.
Genetic counselling
Genetic counselling is a conversation, not a test. It helps you understand where a risk comes from, what each testing option offers, and what you might do with the answer. You will not be pressed towards any choice, and the decision whether to test always remains yours.
Counselling is useful before testing, when a screening result is higher chance, when a scan shows a structural finding, after a previous pregnancy with a genetic condition, and when parents are blood relatives. A family tree is drawn, earlier reports are reviewed, and the next steps are written down for you.
Good counselling also prepares you for every possible answer before the test, including a no-call result, a finding of uncertain meaning, or an incidental result about a parent’s own health. Knowing this in advance makes the wait for results less stressful and the decisions afterwards clearer.
Thalassaemia, sickle cell and carrier screening
Beta-thalassaemia trait is common in Gujarat, carried by roughly 3 to 8% of people in different communities. If both parents carry it, each pregnancy has a 1 in 4 chance of thalassaemia major. An HPLC blood test early in pregnancy, ideally for both partners, identifies carriers. A low MCV on a routine blood count is often the first clue, and it is important not to mistake thalassaemia trait for iron deficiency, as extra iron does not correct it.
Sickle cell disease is common in some tribal communities in Gujarat and follows the same 1 in 4 pattern. When both partners are carriers, CVS at 11 to 13 weeks can test the baby directly by DNA analysis. Carrier testing for conditions such as spinal muscular atrophy, or targeted testing where a family mutation is known, can be discussed, ideally before conception.
Diagnostic genetic tests
A diagnosis needs a sample from the pregnancy: CVS from 11 weeks or amniocentesis from 15 weeks. Rapid tests (QF-PCR or FISH) give results for the common trisomies in 2 to 3 days. Karyotype looks at the whole chromosome set, while chromosomal microarray detects smaller missing or extra pieces and finds an additional cause in about 6% of babies with a structural finding and a normal karyotype.
When a scan shows a structural finding with a normal microarray, exome sequencing may identify a single-gene cause in some cases. Results can include variants of uncertain significance, which are discussed carefully before testing.
Planning ahead: future pregnancies and care at the hospital
After a pregnancy with a chromosomal condition such as trisomy 21, the chance of it happening again is usually about 1% or the age-related figure, whichever is higher, unless a parent carries a balanced translocation, which is checked by a parental karyotype. For single-gene conditions the recurrence can be 25% or 50%, and early CVS, or IVF with embryo testing, can be discussed before the next pregnancy.
A pre-pregnancy visit is the ideal time for thalassaemia and other carrier testing, starting folic acid and reviewing family history, especially for couples who are blood relatives.
At Divine Women’s Hospital, Gota, counselling, the NT and anomaly scans, and CVS or amniocentesis when needed are all coordinated by Dr. Devang Patel, so you are not passed between separate clinics. Samples are processed by accredited genetic laboratories, and every report is explained to you in person.
A note on the PCPNDT Act
Pre-natal sex determination is prohibited in India under the PCPNDT Act. The sex of the baby is not detected or disclosed at any scan.
Your care, step by step
- Pre-test counsellingYour history, family tree, scan findings and test options are reviewed so you can choose what suits you.
- Dating or NT scanThe pregnancy is confirmed as viable, dated and checked for twins or a vanishing twin, which affect NIPT.
- Blood sampleA single maternal blood sample is taken from 10 weeks and sent to an accredited laboratory.
- Results discussionResults are explained in person, usually within one to two weeks, with a written summary.
- Further testing if neededIf a result is higher chance or the scan shows a finding, CVS or amniocentesis and further counselling are arranged.
When to book a visit
- You would like a more sensitive screen for Down syndrome than the combined test
- Your NT, double marker or quadruple test result was higher chance
- You or your partner carry thalassaemia trait, sickle cell trait or another inherited condition
- A previous baby had a chromosomal or genetic condition
- You and your partner are blood relatives
- You are planning a pregnancy and want carrier testing first
Warning signs - get same-day care
- Heavy vaginal bleeding or passing clots in early pregnancy
- Severe or one-sided abdominal pain, especially with dizziness or shoulder-tip pain
- Fever, chills or leaking fluid in the days after CVS or amniocentesis
- Cramping that becomes regular or severe after an invasive test
- Vomiting so persistent that you cannot keep fluids down
Labour and emergency care are available 24 × 7. Call the hospital and come in directly.
Myths and facts
Myth: NIPT is a diagnostic test, so a high-risk result is final.
NIPT is screening. Higher-chance results can be false, especially in younger women, and must be confirmed by CVS or amniocentesis.
Myth: With NIPT, the NT and anomaly scans are not needed.
NIPT does not look at the baby’s structure, and about half of serious structural conditions occur in babies with normal chromosomes. Both scans remain important.
Myth: Thalassaemia minor in one parent is harmless, so the other need not be tested.
If both partners carry the trait, each baby has a 1 in 4 chance of thalassaemia major. Testing the partner is essential.
Myth: Genetic counselling means being told to end the pregnancy.
Counselling gives information and options. Every decision, including not testing, belongs to the couple.
Frequently asked questions
How accurate is NIPT for Down syndrome?
In published studies, NIPT detects about 99 in every 100 pregnancies with Down syndrome, with a false-positive rate of around 1 in 1,000. A higher-chance result must still be confirmed by CVS or amniocentesis.
When can NIPT be done?
From 10 weeks onwards. Many couples combine it with the 11–14 week NT scan, which checks early anatomy at the same time.
Should I choose NIPT or the double marker test?
For the common trisomies, NIPT has a higher detection rate and fewer false positives. The double marker comes with the NT scan and can include pre-eclampsia screening, which NIPT does not. Your options are discussed at counselling.
Can NIPT be done in twins or IVF pregnancies?
Yes in IVF pregnancies. In twins it is available with some reduction in accuracy, and it is less reliable after a vanishing twin, which is checked on scan first.
What does a no-call NIPT result mean?
The laboratory could not give a reliable result, usually because the fetal fraction was too low. It happens in a small proportion of tests, more often with higher body weight or very early testing. Options are a repeat sample or another type of screening.
Is NIPT done on an empty stomach?
No fasting is needed. It is a routine blood draw from your arm.
Does NIPT tell the sex of the baby?
No. Under the PCPNDT Act the sex of the baby is not tested for or disclosed, and NIPT reports for pregnancies in India do not include it.
My husband and I are both thalassaemia carriers. What should we do?
Each pregnancy has a 1 in 4 chance of thalassaemia major. CVS at 11 to 13 weeks can test the baby directly. Planning before pregnancy also allows discussion of IVF with embryo testing.
What is a variant of uncertain significance?
It is a genetic change whose effect is not yet known. It is not a diagnosis, and parental testing often helps clarify it. This is discussed before microarray or exome testing.
My NIPT is low risk but the scan shows a finding. What does that mean?
A low-chance NIPT makes the common trisomies unlikely, but it does not exclude smaller chromosomal changes or single-gene conditions. When a scan shows a significant structural finding, amniocentesis with microarray is usually offered regardless of the NIPT result.