NIPT is a simple blood test from the mother that can screen for some chromosomal conditions in the baby, from about 10 weeks of pregnancy. It is very accurate for some conditions, but it is still a screening test, not a diagnosis.
Imagine your combined screening result comes back as “higher chance” for Down’s syndrome. You are offered either an amniocentesis or an NIPT blood test. You want answers, but you are frightened of any risk to the pregnancy.
What NIPT is
During pregnancy, small fragments of DNA from the placenta circulate in the mother’s blood. Non-invasive prenatal testing (NIPT), also called cell-free DNA screening, analyses these fragments to estimate the chance that the baby has certain chromosomal conditions.,Because it only needs a blood sample from the mother, NIPT carries no risk of miscarriage.
What NIPT screens for
- Down’s syndrome (trisomy 21)
- Edwards’ syndrome (trisomy 18)
- Patau’s syndrome (trisomy 13)
- Some tests also look at sex chromosome conditions and the baby’s sex
- Some private tests offer extra screens, which may be less accurate
When it is offered
In some health systems, NIPT is offered to everyone. In others, it is offered as a second step when the combined or quadruple screening test shows a higher chance. It is also available privately in many countries. It can usually be done from 10 weeks of pregnancy.
How accurate is it?
NIPT is very good at detecting Down’s syndrome, picking up the large majority of affected pregnancies. It is slightly less accurate for Edwards’ and Patau’s syndromes.,However, NIPT can still give false results. A “high chance” result is not a diagnosis, especially in lower-risk pregnancies. The result can be affected by changes in the placenta that are not present in the baby, or by twins, obesity or certain maternal conditions.
Understanding a “high chance” result
If NIPT shows a high chance, you will usually be offered a diagnostic test, such as chorionic villus sampling (CVS) or amniocentesis, to confirm or rule out the condition. These tests analyse cells from the placenta or amniotic fluid and give a definite answer, but carry a small risk of miscarriage. Professional guidelines advise against making decisions about ending a pregnancy based on NIPT alone.
Understanding a “low chance” result
A low-chance result means it is very unlikely the baby has the conditions screened for. It does not rule out all chromosomal or genetic conditions, or physical conditions such as heart defects, which is why the 20-week anomaly scan is still important.
No result
Sometimes NIPT cannot give a result, often because there is not enough placental DNA in the sample. This is more common early in pregnancy and in women with a higher body weight. You may be offered a repeat test.
Making your decision
- Screening is always your choice
- Think about what you would want to do with the results
- Ask about the accuracy for your situation and the costs
- Talk to your midwife, healthcare provider or a genetic counsellor
- Support organisations can provide balanced information about living with these conditions
Diagnostic tests: CVS and amniocentesis
If screening suggests a higher chance of a chromosomal condition, diagnostic tests can give a definite answer. Chorionic villus sampling (CVS) is usually done between 11 and 14 weeks and takes a small sample of the placenta, through the tummy or occasionally through the cervix. Amniocentesis is usually done from 15 weeks and takes a small amount of the fluid around the baby through a fine needle in the tummy.
Both tests are done using ultrasound guidance. They carry a small risk of miscarriage, which experienced centres estimate at well below 1 in 100. Results for the main chromosomal conditions are often available within a few days, with full results taking longer.
Living with Down’s syndrome today
When considering screening, it can help to know that life expectancy and opportunities for people with Down’s syndrome have improved greatly in recent decades. Many people with Down’s syndrome attend mainstream schools, work, have relationships and live semi-independently. Each person is different, and some have health conditions, such as heart problems, that need treatment. Support organisations can share real experiences to help you make an informed choice.
Getting support with decisions
Decisions about screening and diagnostic tests are personal, and there is no right or wrong choice. Some people want as much information as possible during pregnancy; others prefer not to have screening. You can ask to speak to a specialist midwife, a fetal medicine specialist or a genetic counsellor, and take time to think. Your choices will be respected.
Questions to ask before NIPT
- Which conditions does this test screen for?
- How accurate is it for my age and situation?
- What will happen if the result is high chance or no result?
- Is it free, or will I need to pay?
- How long will results take?
Frequently asked questions
Does NIPT tell me the sex?
Some tests can, if you ask. Rules vary by country.
Is NIPT available for twins?
Some tests can be used in twin pregnancies, but accuracy may differ.
Does NIPT replace the 20-week scan?
No. The scan checks the baby’s physical development, which NIPT cannot do.
But a private clinic offers a “full genome” screen. Is that better?
Extra screens often have higher false-positive rates. Discuss them with your healthcare provider or a genetic counsellor before paying.
Your next step: If you are offered NIPT, ask how accurate it is for your situation and what the next step would be after each possible result.
Related: The 12-week dating scan · The 20-week anomaly scan
Sources: NHS Fetal Anomaly Screening Programme, American College of Obstetricians and Gynecologists, International Society for Prenatal Diagnosis, Royal College of Obstetricians and Gynaecologists.
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