Non-Oncology Applications: 1 of 14

Non-Invasive Prenatal Testing (NIPT)

During pregnancy, the placenta, the organ that connects the developing baby to the mother's blood supply, is constantly shedding cells. As those cells break down, they release DNA into the mother's bloodstream. By around the tenth week of pregnancy, enough of that DNA is usually present in a blood sample to measure. Because it comes from the pregnancy rather than from the mother, it can provide information about the developing baby.

The most common use is checking chromosome number. Chromosomes are packages of genetic instructions, and people normally have 46 of them, arranged in 23 pairs. Sometimes a pregnancy has an extra copy of one chromosome, which can affect development. Down syndrome, for example, is caused by an extra copy of chromosome 21. NIPT works by counting DNA fragments from each chromosome very precisely. If chromosome 21 contributes slightly more fragments than expected, that can point to an extra copy.

NIPT is by far the most widely used liquid biopsy in routine medical care. It is offered routinely in many countries and has reduced the need for amniocentesis, a procedure in which a needle is passed through the abdomen into the fluid around the baby. Amniocentesis can give a definite answer, but it also carries a small risk of miscarriage. A blood draw does not carry that procedure-related risk.

A high-risk NIPT result still needs confirmation because NIPT is used for screening rather than diagnosis. The confirming test is often amniocentesis. The blood result by itself is not definitive.

The DNA also comes from the placenta rather than directly from the baby. In almost all pregnancies, the two are genetically the same. Occasionally a genetic change is present in the placenta but not in the baby. In that situation, the blood test can correctly report what is happening in the placenta while giving the wrong impression about the baby.

As with other forms of screening for rare conditions, the meaning of a positive result depends partly on how common the condition is. For very rare conditions, a larger share of positive results can turn out to be false alarms even when the test itself performs well.