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Also known as a sonogram, an ultrasound reflects sound waves off of the fetus and then is shown on a special computer screen. This test is not very clear and physical features such as limb, heart, brain, and spine abnormalities can't be seen until 16-18 weeks of p ....

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.... because it is of fetal origin. Chorionic villus sampling will detect up to 99% of chromosome abnormalities. Some follow-up ultrasounds are recommended at 16 weeks of pregnancy. The amount of risk is the same as in amniocentesis. Amniocentesis Amniocentesis is performed at 15-20 weeks of pregnancy. It will detect chromosome abnormalities and other certain genetic disorders. This test can detect up to 95% of neural tube disorders such as spina bifida. It is done by inserting a needle near but not through the woman's naval into the amniotic sac. A small amount of amniotic fluid is withdrawn and sent for laboratory testing. Cells are then separated fro ....