Genetic disorders can be screened during pregancy in several ways. The two most common methods are amniocentesis and chorionic villus sampling. Amniocentesis analyzes the amniotic fluid and can identify gender as well as some genetic disorders. Chorionic villus sampling analyzes a small piece of the placenta, and can identify some genetic disorders. Both of these methods are invasive, and carry the risk of inducing a miscarriage, and both are perfomed several months into the pregnancy. In cases of in-vitro fertilization, a cell from the embryo can be analyzed before the embryo is inserted; this is called Preimplantation Genetic Diagnosis.
A recent study showed that testing the blood and saliva of the parents could also help screen genetic disorders. This procedure, which is currently called Noninvasive Fetal Whole-Genome Sequencing, is completely non-invasive, and can be carried out without testing the fetus itself in any way; it also can be performed much earlier in the pregnancy than other procedures. However, this procedure is not approved for use yet, and other studies are proceeding.