NIPT: Paving the Way for Thousands of DNA Tests

Non-invasive prenatal testing (NIPT) is a maternal blood test that analyzes DNA from the placenta found in the mother’s bloodstream. A relatively new medical advance, NIPT is so revolutionary because placental DNA is identical to the DNA of the developing fetus. Results from a non-invasive prenatal screening test determine if there is a risk that the child may have a chromosomal abnormality, such as Down syndrome.

The use of prenatal genetic testing began over 60 years ago, but testing wasn’t always non-invasive, and didn’t always have the ability to look for genetic abnormalities. Early prenatal tests involved collecting tissue from the uterus to determine the baby’s gender. Today, laboratory technicians are able to analyze certain substances in the mother’s blood using various NIPT tests, like MaterniT® 21 PLUS, to screen for chromosomal abnormalities in the baby’s DNA. This reviews the historical path to non-invasive prenatal testing and provide a glimpse of what’s possible for the future of prenatal screening.

The Beginning of Prenatal Genetic Testing

Before non-invasive prenatal testing, the standard prenatal genetic tests were amniocentesis and chorionic villus sampling (CVS). Amniocentesis requires inserting a needle either through the abdomen or the cervix to collect a sample of amniotic fluid for genetic analysis. The first detailed description of amniocentesis was published in 1956. At first, this procedure was used to determine the sex of the baby, but it was then expanded to detect genetic conditions, like muscular dystrophy.

CVS involves collecting a sample of DNA directly from fetal cells found in the placenta by inserting a needle either through the abdomen or the cervix to collect a tissue sample. In 1968, the first attempt at chorionic villus sampling was made, but it wasn’t until 1984 that a safer method for CVS sampling was implemented into standard care.

Both CVS and amniocentesis are associated with increased risk to the health of the fetus due to their invasive nature. For this reason, scientists searched for a non-invasive method for fetal DNA analysis.

Hormones Found in Maternal Serum Indicate the Health of the Fetus 

Scientists made a breakthrough when they discovered patterns between hormones and proteins found in the mother’s bloodstream and certain chromosomal conditions or physical abnormalities in babies. The first relationship observed between substances found in the mother’s bloodstream and chromosomal abnormalities in a fetus was recognized in 1984.1 In a study of pregnant women that looked at their probability of having a child with a chromosomal abnormality, lower levels of a protein called alpha-fetoprotein (AFP) were associated with an increased risk of chromosomal abnormalities in the fetus that prevented fetal development.

This discovery led to advancements in maternal screening tests. Today, a blood sample from the mother is used to analyze hormone levels in her bloodstream. The levels of these hormones determine the risk of either chromosomal abnormalities or structural abnormalities, like problems with brain or spinal cord development, in the fetus.

Other hormones in the mother’s bloodstream linked to the health of the fetus were later identified, including:

Estriol, produced by the placenta and the baby's liver

Human chorionic gonadotropin (HCG), produced by the placenta

Inhibin A produced by the placenta

Cell-Free DNA from the Fetus Discovered in the Mother’s Bloodstream

In 1997, a group of scientists discovered that fetal DNA circulates through the mother’s bloodstream throughout pregnancy.2 This knowledge motivated scientists to develop a non-invasive way to screen for chromosomal abnormalities without the risks associated with invasive procedures. This test was called non-invasive prenatal testing, or NIPT.

Today, NIPT is highly accurate. For instance, according to the Centers for Disease Control and Development, NIPT has a 98 percent accuracy rate and a 0.5 percent false-positive rate in detecting Down syndrome.3 The accuracy of non-invasive screening has eliminated the need for invasive testing, like amniocentesis and CVS, as a first-line testing option. Now, these tests are reserved for women who receive a high-risk result from a non-invasive prenatal screen. If a non-invasive prenatal screening indicates that there is a high risk that the child may have a chromosome disorder, couples have the option of invasive diagnostic testing to receive a definitive diagnosis.

The Future of Prenatal DNA Testing

The discovery of cell-free fetal DNA has led to great advances in prenatal screening technology. Today, scientists are working on being able to screen for a wider range of conditions early on in pregnancy and offering affordable testing options.

Sources:

  1. Merkatz I, Nitowsky H, Macri J, Johnson W. An association between low maternal serum α-fetoprotein and fetal chromosomal abnormalities. American Journal of Obstetrics & Gynecology. April 1, 1984; Volume 148, Issue 7: Pages 886–894.
  2. Lo YM, Corbetta N, Chamberlain PF, Rai V, Sargent IL, Redman CW, Wainscoat JS. Presence of fetal DNA in maternal plasma and serum. Lancet. 1997 Aug 16;350(9076):485-7.
  3. NIPT:Beyond the Basics. Centers for Disease Control and Prevention. https://ftp.cdc.gov/pub/CLIAC_meeting_presentations/pdf/Addenda/cliac1115/10_Bellcross_Genetics_NIPS_CLIAC_Nov2015.pdf. Publication date November 2015. Update unavailable. Accessed August 03, 2018.

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