Who Is Eligible For First Trimester Screening?
First trimester screening is designed to detect chromosomal abnormalities in low-risk pregnancies in younger mothers. Women older than 34 as well as couples with additional risk factors may also consider other diagnostic testing procedures, such as Amniocentesis or Chorionic villus sampling (CVS). Second Trimester maternal serum screening for fetal open neural tube defects and aneuploidy Maternal serum screening has been modified during the past 25 years and is now widely utilized during the second trimester to identify women at risk for fetal open neural tube defects (ONTDs), anencephaly, and trisomies 21 and 18. NEURAL TUBE DEFECTS In the 1980s maternal serum screening programs became available to identify pregnancies at risk for ONTDs and anencephaly; 75-90% of ONTDs and >95% of anencephalics can be detected by elevated maternal serum alphafetoprotein (MSAFP) levels. MSAFP screening may also detect fetal abdominal wall defects. The optimal time for NTD screening is 16-18 weeks’ gest
