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MS WordPerinatologist Corner - C.E.U/C.M.E. Modules
Prenatal Genetic Screening – Serum and Ultrasound
Sponsored by The Indian Health Service Clinical Support Center
2. Background
The risk of having a child with Down syndrome (trisomy-21)
increases with increasing maternal age, but at present, the majority of Down syndrome (DS) children are born to younger women, as they are who have the majority of the babies (see more on demographics below). Various tables are available for calculating the risks of fetal aneuploidy by maternal age. (Aneuploidy refers to an unbalanced chromosome make-up, e.g., an extra chromosome 21, resulting in the Down syndrome phenotype.) Roughly, the risk of DS at age 35 is approximately 1 in 270, which increases to about 1 in 100 at age 40, and to almost 1 in 12 at age 45. When counseling the patient, remember, “is the glass half empty or is it half full?” A 40 year old woman still has 99 out of 100 chances that her child will not be affected!
Maternal serum screening for fetal neural tube defects with elevated alpha-fetoprotein (AFP) has been available since the late 1970’s,
and screening for fetal trisomies, initially with decreased AFP, and then with the combined “triple test” (AFP, serum human chorionic gonadotrophin [bHCG], and unconjugated estriol [uE3]) since the early and late 1980’s respectively. Currently, the “quad screen”, adding dimeric inhibin-A as a fourth analyte, has shown advantages. At the present time it has become standard of care to offer such screening in the second trimester, and about 70% of women currently opt for testing. Counseling the pregnant woman about whether multiple marker screening (MMS) is something she wants, and then what to do if her screen returns with an abnormal result, have become components of prenatal care. The process can be time-consuming, at times confusing, and often very anxiety producing.
