Approximately one in every 700 pregnancies in the United States involves an abnormality of the chromosomes, a condition that results in incurable medical conditions such as Down syndrome. Tests for chromosomal abnormalities can be done during pregnancy but they are not always reliable, some come with a risk to the pregnancy, and can’t be done until the pregnancy is well advanced. The latest edition of the New England Journal of Medicine includes the story on a DNA test that is ten times more accurate than those in wide use today and it can be done much earlier in the pregnancy, too.
Currently, diagnosis of chromosomal abnormalities is a two-part process. Blood tests and ultrasound scans can offer a hint of concern but no diagnosis. When these preliminary tests indicate the need for further testing, amniocentesis or chorionic villus sampling (CVS) are done. Amniocentesis requires removal of a tissue sample from the fetus for biopsy and CVS requires tissue from the placenta. Retrieving these tissue samples can jeopardize the pregnancy.
The newer, more accurate fetal DNA test described in the journal study is manufactured by Illumina Inc., a company in California that also sponsored the study conducted at Tufts Medical Center in Boston. Dr. Diana W. Bianchi, Executive Director of the Mother Infant Research Institute at the Tuft’s Floating Hospital for Children, has done consultation work with Illumina in the past.
The Bianchi study involved 1,914 pregnant women who were screened for chromosomal abnormalities the traditional way and with the Illumina test.
- Both testing methods identified eight pregnancies with chromosomal abnormalities.
- Five of those eight abnormalities were Down syndrome.
- Traditional testing produced a false alarm rate for Down syndrome at 3.6%.
- The Illumina DNA screening produced a false alarm rate at 0.3%.
The Illumina test can be done during weeks 9 and 10 of gestation but other screening procedures must be done later in the pregnancy. The earlier diagnosis could allow pregnancy termination earlier and more safely when a severe abnormality is detected.
The DNA test is expensive ($1,200 to $2,700) in comparison to ultrasound ($200 to $300) and blood tests now in use ($300 to $400) but it could eliminate the need for as many as 200,000 riskier invasive tests in the US each year. Insurance coverage for any fetal screening test varies according to provider and circumstances of pregnancy.
Some members of the medical community say the Tufts study is too small to prove the merits of the Illumina test in the general population but more, larger studies are in progress. Another concern is that about a third of the women in the Tufts study group were in the third trimester of pregnancy when tested; speculation remains as to its accuracy in earlier stages.
Source: “Study shows non-invasive prenatal DNA tests more accurate than current screenings.” Tufts Medical Center News & Events. Tufts Medical Center. Feb 26, 2014. Web. Mar 6, 2014.