To assess the risk of a pregnant woman's developing baby (fetus) having certain chromosome disorders, such as Down Syndrome. NIPT is currently available through routine NHS antenatal services in the UK. However, only women who are at a higher chance of having an affected pregnancy following initial First Trimester or Second Trimester screening will be offered the test.
Please see the Antenatal Results and Choices website for more information on accessing the NIPT privately.
The test is most accurate during or after the 10th week of pregnancy but can be performed at any time up to 22 weeks..
A blood sample taken from a vein in the mother's arm. The test is termed “Non-invasive” because obtaining the sample carries very little risk to the mother or baby, unlike procedures such as Amniocentesis and Chorionic Villus Sampling (CVS).
No test preparation is needed.
Non-Invasive Prenatal Testing (NIPT) is a relatively new test that may be used to assess the risk of a pregnant woman's developing baby (fetus) having a chromosome disorder, such as Down syndrome (trisomy 21), Edwards syndrome (trisomy 18), or Patau syndrome (trisomy 13). It may be used to identify other rare conditions caused by the presence of an extra chromosome or a missing piece of a chromosome (microdeletion).
The test involves looking at cell-free fetal DNA (cffDNA), which is genetic material released by the placenta that circulates in a woman's blood during pregnancy. It is detectable in a pregnant woman's blood in very small quantities from the later stages of the first trimester. CffDNA generally reflects the genetic makeup of the developing baby.
For women using NHS services the test is currently available only if initial First Trimester or Second trimester screening suggests the pregnancy is at a higher chance of being affected by a chromosomal anomaly. The test is also offered privately by several commercial suppliers.
NIPT can only be used as a screening test, not a diagnostic test. If there are abnormal findings from routine prenatal testing or NIPT, then more invasive confirmatory testing using procedures such as chorionic villus sampling (CVS) or amniocentesis may be required to confirm the diagnosis.
Non-Invasive Prenatal Testing is generally only suitable:
A negative NIPT result for trisomy 13, 18 or 21 means that it is very unlikely that the baby has any of these conditions, but other abnormalities may still be present. If the test is positive there is a very high risk that the baby is affected by the identified abnormality but the test is not good enough to say for certain and further invasive testing is required for confirmation i.e. Chorionic villus sampling (CVS) between 10 and 15 weeks of pregnancy or amniocentesis between 15 and 20 weeks of pregnancy.
The full range of applications of cffDNA analysis has yet to be established. As research progresses, use of the test may be expanded to many other abnormalities.
If a woman is tested prior to the tenth week of pregnancy, it is possible to get a false-negative result because of insufficient cffDNA circulating in the mother's blood e.g. low concentration of fetal DNA in the mother’s blood.
Obesity can lower the concentration of cffDNA in a mother's blood and can mean there is insufficient amounts for accurate testing. Some women may therefore find that they cannot be given a result.
There are some circumstances in which NIPT cannot be performed, such as in women with cancer or with certain blood disorders.
Rarely, more than one set of genetic information (cell lines) may be present in the placenta, so a trisomy could potentially be present in some cells but not others. This is known as "confined placental mosaicism" and it could affect NIPT results.
For women using NHS services the test is currently available only if initial First Trimester or Second trimester screening suggests the pregnancy is at a higher chance of being affected by a chromosomal anomaly. The test is also offered privately by several commercial suppliers.
More information about access from within the UK can be found on the Antenatal Results and Choices website.
The RAPID study demonstrated that NIPT is beneficial and cost effective but only when introduced in addition to standard screening i.e. testing after an initial high risk result from existing first or second trimester screening. Whilst the test is highly sensitive and specific it is not currently cost effective for use as ‘first line’ screening test for low risk women. Existing first trimester screening also provides additional information that can be useful in assessing the health of a pregnancy.
Cell free DNA originating from many different sources has been identified. Detecting fetal DNA in a mother’s blood is just one application of the technology. Another major area of interest is around the detection and management of some cancers. Research is currently being carried out on the measurement of circulating cell-free DNA (ccfDNA) released into the blood by cancer cells (sometimes called a "liquid biopsy"). Cancer cells and their genetic material are different from normal cells. Most cancers are currently diagnosed by taking a biopsy of tumour tissue and evaluating it under the microscope for characteristic cellular differences. The clinical utility of ccfDNA testing has yet to be fully determined, but it has the potential to help diagnose cancers early using a blood sample to obtain ccfDNA, helping to distinguish between benign and malignant tumors, determine a likely prognosis, and to monitor the effectiveness of treatment.