Amnio or CVS. Typically the term "invasive prenatal diagnosis" applies to two tests commonly performed to obtain fetal genetic information, amniocentesis and chorionic villus sampling. The word "invasive" is used for procedures like these because the uterus is entered through a needle into amniotic sac or through a catheter into placental tissue, respectively.
Genetic testing. Prenatal diagnostic testing usually involves obtaining fetal tissue from the uterus. That is typically done early (about 9 to 11 weeks) in a pregnancy by chorionic villus sampling and later (15 weeks or later) by amniocentesis.
Ultrasound. Noninvasive means test being performed does not enter the body i.e. Down the throat/airway, up the vaginal canal, anal canal, or piercing through the skin/tissue such as entering blood vessels, abdominal cavity etc... An ultrasound done without having to do above is noninvasive--such as checking gallbladder for stones etc...
Without risk to fetu. New technology instead of getting a tissue sample from the fetus or amniotic fluid by using needles, just from mother's blood fetal blood cells can be extracted. These fetal cells then are tested for genetic conditions. Common noninvasive studies are fetal ultrasounds or mri's; images of fetal body parts can lead to a diagnosis. Maternal serum tests are only screening studies, not to diagnose.