Triple or quadruple screen and neural tube defects

The alpha-fetoprotein (AFP) part of the triple or quadruple screen test estimates your risk of carrying a fetus with a neural tube defect such as spina bifida, abdominal wall defect, or certain types of genetic disorders.

The risk of having a baby with a neural tube or abdominal wall defect does not increase with a mother's age. In women of all ages, the risk of having a baby with an open neural tube defect is most influenced by their folic acid intake, high blood sugar related to diabetes, or high body temperature during the first 28 days of fetal growth and some rare inherited conditions.¹ The risk of neural tube defects also increases if the mother takes certain antiseizure medications while pregnant.

The triple screen and follow-up diagnostic tests can detect most, but not all, neural tube defects.

• Most women have a screen-negative result for neural tube defects.² This means that the triple screen shows no increased risk that a fetus has a neural tube defect.
• Of women whose alpha-fetoprotein (AFP) level is high (suggesting a neural tube defect), only 1 in 16 to 1 in 33 actually has an affected fetus.¹ These women can then have fetal ultrasound or amniocentesis to see whether the fetus has a birth defect.
• Overall, the triple screen helps detect 80% of fetuses with open spina bifida and 97% of those with anencephaly.² A follow-up amniocentesis provides a definitive diagnosis.

Citations

1. Cunningham FG, et al. (2005). Prenatal diagnosis and fetal therapy. In Williams Obstetrics, 22nd ed., pp. 313–339. New York: McGraw-Hill.

2. Genetic Disease Branch, California Department of Health Services (2007). The California Expanded AFP Screening Program. Richmond, CA: California Department of Health Services. Also available online: http://www.dhs.ca.gov/pcfh/gdb/html/ps/ETREnglish2007.pdf.