ALPHA FETOPROTEIN SCREENING (AFP)
Enhanced AFP. Beginning in the early 1980s, pregnant women were offered Alpha-fetoprotein
(AFP) screening to detect neural tube defects such as spina bifida (open spine)
as well as Down syndrome. In the late 1980s the test was enhanced to also measure
the levels of two pregnancy hormones: estriol and human chorionic gonadotropin
(HCG). This new and improved test is commonly known as the Enhanced AFP, AFP3,
or a triple screen.
The screening is done 16 to 18 weeks after the last menstrual period. The test
is routine and poses no threat to mother or baby. Blood is drawn from the mother's
arm and sent to a laboratory for testing. Results are normally available in
one week, depending on the laboratory used.
Maternal serum Alpha-fetoprotein (MSAFP) is produced by the liver of the fetus
and enters the mother's bloodstream. Elevated levels of MSAFP may mean a neural
tube defect or absence of all or part of fetal brain material, otherwise known
as anencephaly. Triple screening can diagnose a high percentage of anencephaly
and spina bifida cases. A low level of MSAFP could be an indication of Down
syndrome; however, an AFP screen is not as accurate as an amniocentesis or chorionic
villus sampling (CVS) in detecting Down syndrome, according to R. Harold Holbrook,
Jr., M.D. of Stanford University. Only an amniocentesis or CVS screen can definitely
diagnose or exclude Down syndrome. An AFP test can show a risk of an abnormality,
not a diagnosis.
On a happy note, an elevated MSAFP level could also mean twins have been conceived,
according to the Inland Northwest Regional Perinatal Center. A miscalculated
due date can cause an elevated level, too.
Additional testing is performed in the event of an abnormal AFP test result
and genetic counseling is available for the parents. According to the Cleveland
Clinic Health Information Center, for every 1,000 mothers tested, 25 will have
an abnormal test result. However, out of those same 25 abnormal results, only
one or two will have a confirmed result of an abnormal fetus after further testing
is completed. Even with those statistics, an abnormal test result can bring
panic and anxiety to an expecting couple.
Dr. Jacob Canick is the lab director at the division of prenatal and special
testing for the department of pathology at Women & Infants Hospital of Rhode
Island. The facility is the primary teaching affiliate of the Brown University
School of Medicine for obstetrics, gynecology and newborn pediatrics. Canick
explains that the AFP3 test is a triple-marker test, checking the protein hormones
AFP, estriol and HCG. He and his team of researchers have developed a four-marker
test, the AFP Quad test, which can also detect high levels of a fourth protein
hormone called Inhibin A.
"Inhibin A and HCG protein hormone levels tend to be high and ASP and
estriol protein hormone levels tend to be low in the event of a fetus with Down
syndrome," Canick says. Please note that although the new ability to check
this fourth hormone increases the accuracy of the test, an abnormal result may
not be a sure sign of fetal abnormalities. The AFP Quad test is not yet available
in all areas.
Steve and Marian King from Long Beach, Calif., were delighted to find out that
they were expecting their third child. The good news came at a difficult time
for the couple. Marian's mother was terminally ill and Marian spent the first
several weeks of her pregnancy at her mother's bedside.
The couple received an abnormal AFP test result two weeks after Marian's mother
passed away. Marian and Steve were referred to a genetic counselor and were
fortunate enough to get an appointment the very next day. The plan was that
the counselor would meet with Marian and Steve for an hour, then an ultrasound
would be performed to view the fetus. Within a few moments into the ultrasound,
Steve asked, "Do I see two heads?" Five months later, Marian gave
birth to healthy twin boys. (by Sharon Waldrop)
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