The 2nd trimester signals a new round of prenatal testing. During one of your routine visits between 15 weeks and 20 weeks, your health care provider may offer to draw blood for a "multiple marker" screening test, also known as a quad marker screen. This screen indicates if the fetus is at risk of having a chromosomal abnormality; it identifies about 75 percent of babies with Down syndrome and 80 percent of infants with neural tube defects such as spina bifida.
Although it's never fun to have another needle in your arm, this screening test can help you decide whether to have an amniocentesis, which is a more invasive test with a higher risk to your baby. After your blood is drawn, it will be sent to a laboratory and tested for four different biochemical markers: alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), unconjugated estriol (uE3), and inhibin-A.
The results of a multiple marker screen are typically available within seven working days, when your provider will receive either a "screen positive" or "screen negative" test result. If you test positive on this screen, you'll be offered an ultrasound and possibly an amniocentesis for a definitive diagnosis.
Originally published in You & Your Baby: Pregnancy.
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