Prenatal screening is an important part of any pregnancy. Typically, noninvasive techniques, such as examining Fetal Cells in Maternal Blood (FCMB), ultrasound, or nonstress tests are used to screen for a prenatal condition. Fetal karyotype testing, which detects major chromosomal mutations, is commonly used as a confirmatory test after abnormalities are detected through screening. Chromosomal microarray is another, relatively newer procedure, used in prenatal diagnosis of chromosomal abnormalities. It has been shown to be able to detect more genetic mutations in children compared to regular karyotyping, leading some to think it should be a first-line confirmatory test over karyotyping.
Now, a prospective cohort trial of over 4400 women recently published in the New England Journal of Medicine shows that microarray analyses are equally efficacious as karyotyping in identifying certain chromosomal abnormalities (aneuploidies and unbalanced rearrangements) and may provide additional structural chromosomal findings in patients with normal karyotypes. Microarray testing in fact identified important genetic anomalies missed by karyotyping in nearly 2% of pregnancies with the usual indications for diagnostic testing (such as advanced maternal age) and 6% of cases with abnormal ultrasounds.
According to Dr. Ronald J. Wapner and colleagues of Columbia University Medical Center in New York:
These data indicate a benefit to chromosomal microarray analysis as a standard part of prenatal testing, bearing in mind that, as with karyotyping, the detection of variants of uncertain clinical significance presents a challenge for counseling and cause anxiety [to patients]
This last phrase is important, as microarray detected “uncertain” findings in 3.4% of normal karyotype samples. Interpreting these findings is somewhat discretionary and requires input from laboratory technicians, geneticists, and physicians together. Furthermore, the phenotypic implications and small size of certain mutations must also be taken into account when making these decisions.
Nevertheless, this study shows that microarray may offer a promising new avenue of confirmatory tests for prenatal diagnosis and may be regularly offered to pregnant women. This is consistent with recommendations of the American congress of Obstetricians and Gynecologists (ACOG), which suggests that all women should be offered the option of invasive testing.
Check out the study in the New England Journal of Medicine: Chromosomal Microarray versus Karyotyping for Prenatal Diagnosis
Analysis on ObGynNews.com: Prenatal Diagnosis: Microarray Analysis Bests Karyotyping