Alpha-fetoprotein

Alpha-fetoprotein (AFP) is a protein released by the liver of the fetus. The amount of AFP circulating in the mother’s blood can be used as a screening test for defects in the neural tube development of the fetus such as anencephaly (scant or absent skull) or spina bifida (open spinal cord defect).  It can also be elevated in pregnancies complicated by abnormal closure of the abdominal cavity of the fetus. AFP is measured by a blood test drawn between 15-20 weeks of gestation. If the value is abnormal, you will be sent to the maternal-fetal medicine specialists for a targeted ultrasound that will look closely at the baby’s skull, spine, and abdomen, and offered an amniocentesis that is diagnostic. The false positive rate for AFP screening alone is quite low.

AFP can also be used in combination with other hormonal markers, between 15-20 weeks, to screen for Down syndrome (Trisomy 21) and Trisomy 18. Commonly known as the “quad screen” for the 4 hormones measured, this test has a higher false positive rate and a lower sensitivity than first trimester screening done by ultrasound and hormone screening (Ultrascreen®).  We prefer to do first trimester screening for this reason. However, if prenatal care is started after the window of opportunity for Ultrascreen®, this is an option for screening for trisomies 21 and 18.