Ultrasonography, chorionic villi sampling, and alpha-fetoprotein screening are other prenatal diagnostic screening techniques besides amniocentesis. Fetal ultrasound is often done early in a pregnancy to determine whether it is an ectopic pregnancy. Fetal ultrasound is an accurate way to determine fetal age and predict a due date. Placental abnormalities, fetal growth and development (including heart rate), and congenital abnormalities may be detected with fetal ultrasound. It is a noninvasive test and relatively safe for the mother and fetus.

Chorionic villi sampling is another technique used to detect birth defects, such as Down syndrome or Tay-Sachs disease. It is usually done early in a pregnancy, between the ninth and fourteenth weeks. A sample of cells, called the chorionic villi, is taken from the placenta where it attaches to the wall of the uterus. The chorionic villi are tiny projections from the placenta that have the same genetic material as the fetus. The tissue sample is taken either through the cervix or through the abdominal wall.

The alpha-fetoprotein (AFP) test is a screening test to determine whether a woman is at risk for carrying a fetus with birth defects. AFP is produced by the fetus and appears in the mother’s blood during a pregnancy. Abnormally high amounts of this protein may indicate a problem with the fetus. It is usually done between weeks 16 to 18 in the pregnancy.