The Prenatal Diagnosis Center at Cedars-Sinai is a state-approved alpha-fetoprotein (AFP) prenatal diagnosis center. AFP screening is performed on a blood sample obtained during the 15th and 20th week of pregnancy. It detects about 90% of fetuses with "open structural defects", such as neural tube defects or abdominal wall defects, as well as approximately 60% of babies with Down syndrome and Trisomy 18.
First Trimester Screening
First Trimester Screening uses ultrasound to measure the clear ("translucent") space in the tissue at the back of the developing fetus' neck. This measurement is combines with the measurement of two proteins in a sample of blood to assess the fetuses risk for Down syndrome and other chromosomal abnormalities as well as congenital heart defects. Fetuses with structural or genetic abnormalities often accumulate more fluid at the back of the neck during the first trimester, causing this clear space to enlarge. While the nuchal translucency screening is not a definitive diagnosis, it can help in assessing the need for further invasive diagnostic testing, such as amniocentesis and CVS. The First Trimester Screening must be done between 11 weeks one day, and 13 weeks six days of pregnancy.
It is important to remember that this is a screening test and does not directly test for chromosomal problems. A normal result (called "screen negative") is not a guarantee that your fetus is healthy, but it does suggest that a chromosomal problem is less likely. An abnormal result called ("screen positive") does not mean that your fetus has a definite chromosomal problem, but it does suggest an increase risk for a chromosomal abnormality.