Humans have 23 pairs of chromosomes, totaling 46 chromosomes. One copy of each chromosome is inherited from the mother (egg) and the other from the father (sperm).

• The first 22 pairs are called autosomes and are the same in both males and females.

• The 23rd pair consists of the sex chromosomes. Females have two X chromosomes, while males have one X and one Y chromosome.

An abnormality in an embryo’s chromosomal makeup can result in a specific syndrome or may lead to miscarriage. Sometimes, embryos have an abnormal number of chromosomes—a condition known as aneuploidy.

Aneuploidy is a significant factor in miscarriage, in vitro fertilization (IVF) failure, and various health conditions, including Down syndrome.

The accuracy of NIPT depends on the specific syndrome being screened for. While the test is highly reliable, there remains a very small chance it may not detect an affected pregnancy. Additionally, there is approximately a 0.3% chance of a false positive result. In such cases, we always recommend follow-up diagnostic testing.

NIPT is more accurate than the NHS first-trimester combined test or the second-trimester quadruple test for assessing the risk of genetic conditions. However, it is important to understand that NIPT is a screening tool, not a diagnostic test. Diagnostic procedures such as amniocentesis or chorionic villus sampling (CVS) provide definitive results but carry a risk of miscarriage. Therefore, NIPT is recommended as a safer initial step. Any concerns during pregnancy should be discussed with your healthcare provider.

A negative result does not rule out the possibility of other chromosomal abnormalities, genetic conditions, or birth defects in the pregnancy. There is also a small chance that the test results may reflect the chromosomal makeup of the mother or placenta rather than the baby—a situation known as “placental mosaicism.” Additionally, the presence of a tumour, which can have abnormal chromosome numbers, may affect the results.

A negative result indicates a decreased likelihood of the tested condition. In most cases, the condition is indeed not present (true negative), though rarely, it may still be present (false negative).

A positive result indicates an increased likelihood of the condition. In most cases, the condition is truly present (true positive), but in some instances, it may not be (false positive).

As NIPT is a screening test, results should be interpreted in the context of the overall pregnancy. Positive results should always be confirmed through diagnostic testing before making any pregnancy management decisions.

Please check with a member of our team tests suitable for a multiple pregnancy

Please be aware that a small number of samples may fail the NIPT process if there is insufficient fetal DNA in the mother’s blood for analysis. Testing during the second, third, and fourth trimesters benefits from the lowest failure rates of any NIPT currently available, at approximately 0.1%.