If an initial ultrasound detects potential problems, a more detailed exam may be scheduled. According to the March of Dimes, ultrasound has been used for more than 30 years and no risks have been identified. However, it's not clear that low-risk pregnant women benefit from routine ultrasound exams. In addition, ultrasound can not detect all structural birth defects. Amniocentesis ACOG says amniocentesis is most commonly used in the second trimester to detect birth defects.
Amniocentesis tests a small sample of the amniotic fluid surrounding the fetus.
The March of Dimes says amniocentesis does carry a small risk of miscarriage, so it is not used routinely, but instead when there is an increased risk of chromosomal or genetic birth defects, or certain malformations. Amniocentesis can test for neural tube defects. The neural tube is the part of the developing embryo from which the brain and spinal cord form. The U.S. Public Health Service says it's important for women of childbearing age to get 400 micrograms of folic acid a day in order to help prevent neural tube defects. It may also be appropriate for women if they or a close family member has already had a child with a birth defect.