Who Has Down Syndrome Babies?

Most people associate having a child with Down"false-positives" (test states the patient has the
syndrome with older women. While it is true thatcondition when the patient really doesn't) and
women over 35 do have an increased risk of having"false-negatives" (patient has the condition but the
a child with Down syndrome, 80% of these childrentest states he/she doesn't).
are born to those women under age thirty-five.Maternal Serum Screening
In the United States, approximately 5,000 babies withThe mother's blood is checked for three items:
Down syndrome are born every year. A woman'salpha-fetoprotein (AFP), unconjugated estriol (uE3)
chance of having another baby with Down syndromeand human chorionic gonadotropin (hCG). These three
is approximately 1 in 100.are independent measurements, and when taken
Prenatal Screening for Down Syndromealong with the maternal age (discussed below), can
Over the last 10 years, new technology hascalculate the risk of having a baby with Down
improved the methods of detection of Downsyndrome.
syndrome. While there are ways to diagnose DownA very important consideration in the screening test
syndrome by obtaining fetal tissue samples byis the age of the fetus (gestational age). The correct
amniocentesis or chorionic villus sampling, it would notanalysis of the different components depends on
be appropriate to examine every pregnancy this way.knowing the gestational age precisely. The best way
Besides greatly increasing the cost of medical care,to determine that is by ultrasound.
these methods do carry a slight amount of risk toTest results are sometimes reported to doctors as
the fetus."Multiples of the Median (MoM)." The "average" value
So screening tests have been developed to try tois therefore called 1.0 MoM. Down syndrome
identify those pregnancies at "high risk." Thesepregnancies have lower levels of AFP and estriol, so
pregnancies are then candidates for further diagnostictheir levels would be less than 1.0 MOM.hCG in a
testing.Down syndrome pregnancy would be greater than
Screening Vs Diagnostic Test1.0 MoM.
What is the difference between a screening test andFinally, the calculated risk is used to modify the risk
a diagnostic test? In diagnostic tests, a positive resultalready statistically calculated based on the mother's
very likely means the patient has the disease orage. We already know that as the mother's age
condition of concern. In screening tests, the goal is toadvances, the risk of having a baby with Down
estimate the risk of the patient having the disease orsyndrome increases.
condition.For example: Let's say the test results come back in
Diagnostic tests tend to be more expensive andthe typical range for a pregnancy not associated with
require an elaborate procedure; screening tests areDown syndrome (that would be 1.0 MoM for all
quick and easy to do. However, screening tests havecomponents). This result reduces the woman's risk of
more chances of being wrong: there arehaving a child with Down syndrome four-fold.