Chromosomal abnormalities are present in approximately 1 in 150 live births and risk of aneuploidy increases with maternal age.
Most prenatal testing is intended for screening and the goal is to identify women with fetuses at high risk for chromosomal abnormalities. Numerous options for screening are available and are routinely offered to women during pregnancy. Recent technological advances have led to an expansion in prenatal testing and often couples are facing complex decisions regarding the quantity and quality of information they wish to have regarding their fetus. Thus, as prenatal diagnosis becomes increasingly complex, there is a need for the education of both patients and providers regarding the benefits and limitations of the testing strategies available to them.
Presently, prenatal testing for chromosomal abnormalities usually includes serum screening, ultrasound examination and lately non-invasive prenatal testing (NIPT).
It has been shown that during pregnancy some of the baby’s DNA passes into the mother’s bloodstream. NIPT measures and analyses this cell-free fetal DNA in order to screen for a number of abnormalities and obtain genetic information regarding the chromosomes of the fetus.
Cell-free DNA testing for fetal aneuploidy, constitutes a major advance in prenatal care. Since its introduction in 2011, use of NIPT after the 10th week of pregnancy has been rapidly assimilated into prenatal care in order identify pregnancies at risk with greater sensitivity and specificity than maternal serum screening or first trimester screening. In addition, this test seems to be widely accepted by women.
Although NIPT was originally intended for the prediction of the most common chromosomal trisomies of the fetus (tri. 13, 18, 21) and sex chromosome anomalies, recently it is used for the screening of all chromosomal aneuploidies and a select number of microdeletion syndromes.
As technology improves and the cost of genetic testing decreases, researchers expect that NIPT will become available for many more genetic conditions. It must be emphasized, however, that it is presently considered as a screening test, which means that it can only estimate whether the risk of having a fetus with certain chromosome abnormalities is increased or decreased and a definite diagnosis must always be confirmed by an invasive technique, such as amniocentesis or chorionic villus sampling.