This is a blood test which measures the level of alpha-fetoprotein (AFP) in your blood. It's designed to indicate an increased risk for fetal open neural tube defects, such as spina bifida. It may also indicate an increased risk for Down syndrome. There is a possibility of a "false negative" as well as a "false positive", since no screening test is perfect. This test is usually done between the 16th and 18th week of pregnancy.
