Some HCG testing employs a beta subunit but this is not widespread. A positive screening test suggests only that the risk of DS is increased, and the definitive testing of amniocentesis is indicated. Some ultrasonographers can determine suggestive findings of DS by changes in the neck, or heart. This is not yet confirmed or in wide spread use. Ultrasounds can be normal in a DS fetus.
Earlier testing is thought to be associated with a small risk of fetal limb damage.
The CVS test is done earlier and is usually more rapid than amniocentesis. Amniocentesis, a sampling of the amniotic fluid surrounding the fetus, is routinely done at 14-16 wks.