- Last Update On : 2013-01-20
Maternal serum screening is used to identify pregnancies that may have an increased risk for birth defects such as neural tube defects, Down Syndrome and Trisomy 18. Traditionally, laboratories tested for alpha fetoprotein (AFP), human chorionic gonadotrophin (hCG) and unconjugated estriol (uE3). A pattern of low AFP, high hCG and low uE3 is associated with an increased risk of fetal Down Syndrome.
Recent research has documented that prenatal detection of Down Syndrome can be improved by addition of inhibin A testing. Screening with four markers increases Down Syndrome detection rates without increasing the false positive rate above that encountered with 3 markers. At age 35 years of age, the risk that a woman is carrying a child with Down Syndrome during the second trimester is 1 in 270. Using this risk, four marker screening increases the detection rate for Down Syndrome from 60% with 3 markers to 75 to 80%.