The results of many well-respected studies have shown no ill effects of these sound waves on the fetus or the mother. This examination is available to families who are at risk for certain types of heart defects. An early ultrasound examination is offered from 11 through 13 weeks gestation to measure the width of the fluid filled space behind the fetus's neck. This measurement is used as a screening test to assess the risk for certain chromosome abnormalities, such as Down Syndrome. Because it is only a screen, an abnormal result simply means there is a higher than normal chance for chromosome problem.
Further testing is required to make the specific diagnosis.
Ultrasound is used with the procedures of the amniocentesis and chorionic villus sampling to find the best location for sampling and for guidance of the instruments needed for collecting the cells. During amniocentesis, the fetus and the amniotic fluid are visualized by ultrasonography to guide the needle placement. Amniotic fluid contains loose cells shed by the skin of the fetus. The fluid sample is delivered immediately to the laboratory where the cells are grown into a culture sufficiently large for diagnostic tests. Chromosomes are analyzed and chemical assays and DNA studies are performed as indicated.