In karyotyping, fetal cells are analyzed under a microscope, which allows researchers to see whether too many or too few chromosomes are present, or if the chromosomes have an abnormal structure. In contrast, microarrays compare a sample of the fetus' DNA with that of a healthy person, giving researchers a closer look at the genetic code.
Both tests require fetal cells, which are obtained either by amniocentesis, a procedure that takes cells from the amniotic fluid, or chorionic villus sampling, which takes cells from the placenta. These procedures come with risks, including a small risk of miscarriage.
In the study, Wagner and colleagues analyzed information from about 4,400 pregnant women who had prenatal testing because they were over 35 had an abnormal result on screening test for Down syndrome, or they had an ultrasound that indicated possible birth defects.
Microarray testing was just as good as karyotyping at detecting whether the fetus had too many or too few total chromosomes.
In addition, about 2.5 percent of samples with a normal karyotype had microarray results that revealed missing or repeated sections of genetic code that could result in a genetic disease.
For fetuses with possible birth defects, about 6 percent of samples with a normal karyotype had abnormalities on the microarray.
In a second study, also published today, microarrays more often provided results on genetic…