唐氏症母血篩檢
& 經由母血內一些因懷孕而產生之物質（AFP, b-hCG, free b-hCG etc），配合妊娠週數、母親年齡及體重，而計算出唐氏症之危險機率。
篩檢週數：
目前長庚醫院使用之檢驗方式為：ABBA
（a-fetoprotein, free b–hCG, maternal body weight, gestational age & maternal age）
產前母體血清篩檢報告：
|
姓 名 |
|
病歷號碼 |
|
出 生 日 期 |
|
|
科 別 |
婦 產 科 |
醫 師 |
|
|
|
|
分娩年齡 |
歲 |
母體體重 |
公斤 |
最後月經日期 |
|
|
懷孕週數 |
週 天 |
檢體編號 |
|
採 血 日 期 |
|
結果
free b–hCG (游離型貝他人類絨毛膜性腺激素): ----MoM (中位值倍數) (----ng/ml)
AFP (甲型胎兒蛋白) : ----MoM (中位值倍數) (----ng/ml)
本胎兒患有唐氏症之危險機率為：
本胎兒患有神經管缺損之危險機率為：
說明：
1.
2.
母血篩檢可找出
3. 此種抽血檢驗是一種篩檢方法，並非最後確定診斷方法。
4.
中國人患有神經管缺損之危險機率為
P.S. 除看危險機率外，仍須看APF及free b–hCG之MoM值，決定是否進一步檢查。
WHAT IS AFP TESTING?
AFP testing is a term used to describe a grouping of tests done during
pregnancy. The original reason behind this testing was to find a way to help
pick up certain abnormalities in fetuses. This grouping of tests began during
the 1980's with a blood test that measured the substance alpha-fetoprotein
(AFP). It was found that when this substance is at a high level the fetus often
has a certain type of abnormality such as spina bifida. As researchers
continued to study this type of testing, they began measuring other substances
so that other abnormalities might be identified. Human chorionic
gonadotropin (HCG) and unconjugated estriol (UE3) can be measured along
with AFP. These substances are all produced from the growing fetus and
developing placenta and are found in the blood of all pregnant women. AFP
can be measured in blood or amniotic fluid. HCG and UE3 can only be
measured in blood.
Depending on your provider's preference, the laboratory used and the
woman's personal situation, one (usually AFP) or all of these substances can
be measured. They will be compared to the standard amounts that are
normally present during pregnancy. If all three substances are measured, the
test is referred to as a triple screen or AFP3 . If only AFP and HCG are
measured, the test might be referred to as AFP+ or AFP Plus . Many
providers are choosing to order the triple screen test because the results have
been found to be more accurate when all three substances are measured
compared to when only AFP is measured. Certain fetal conditions will make
the amounts of these substances abnormal or out of balance.
Q. WHY IS AFP TESTING CALLED A SCREENING TEST?
A screening test tells you the likelihood or risk of a problem. It cannot give
you a "yes" or "no" answer. AFP testing is designed to pick out a few women
in the population who are at risk for carrying a fetus with certain problems. It
is NOT a diagnostic test. A diagnostic test is very accurate (it gives you a
"yes" or "no" answer) and medical decisions are made based on definite
results. Since AFP testing is only a screening test, some women will be
identified as being in the at risk group even though they are carrying
NORMAL fetuses . If your AFP test comes back abnormal, you may be one
of the women who has an abnormal result and a normal pregnancy, but were
selected for further evaluation only because of the way the screening process
works.
Q. WHAT FACTORS INFLUENCE THE RESULTS OF THE TEST?
To obtain the result of your AFP test, the laboratory where your sample is
sent uses a formula to calculate the result. Information and facts about you
and your pregnancy are used in this formula. If the wrong information is
given, then the result will be inaccurate.
The information used in the formula includes:
How far along in the pregnancy you are when the sample is taken. This
is usually stated in number of weeks gestation. If there is a question
about how far along you are, an ultrasound examination will confirm
your gestational weeks.
Your weight
Your race
Your age
Family history
The presence of twins
And, insulin dependent diabetes.
Also, if you have had any vaginal bleeding (or occult bleeding within the
amniotic sac, bleeding hidden from the woman's sight) around the time the
AFP blood test sample is drawn, then you are at risk for the test result being
abnormal.
Q. WHAT FETAL ABNORMALITIES CAN AFP TESTING HELP
DETECT?
1. Neural Tube Defects. Neural tube defects are defects in the formation of
the spinal cord and brain. It is called ANENCEPHALY when the defect is at
the top of the head. Fetuses with this condition are often miscarried or die
within several days of birth, as this condition is incompatible with life. SPINA
BIFIDA (or myelomeningocele) happens when the defect is on the lower
part of the back. In this condition, the nerves in the spinal cord do not
connect properly with the nerves in the lower part of the body. This causes
problems with moving lower body muscles. Complications of this condition
may include infections, HYDROCEPHALUS (water on the brain), and
sometimes mental retardation. Infants born with this condition usually require
surgery during childhood. Neural tube defects occur in one or two of every
1,000 pregnancies.
2. Abdominal Wall Defects. Occasionally a fetus will have a defect in the
muscle and skin near the "belly button." This is called OMPHALOCELE or
GASTROSCHESIS and is serious but may be corrected with surgery done
after the birth of the baby.
3. Chromosome Abnormalities. The most common chromosome
abnormality is DOWN SYNDROME, a condition where the fetus has an
excess number of chromosomes. These babies have a distinct appearance
and may have several birth defects -- most commonly, abnormalities of the
heart and some degree of MENTAL RETARDATION that ranges from
minimal to severe. Approximately one in 750 babies born has Down
Syndrome.
4. Other rarer abnormalities, such as kidney or heart problems.
Q. WHAT IF THE AFP TEST RESULT IS ABNORMAL?
First, a review of all the factors that go into the formula used to calculate the
result should be done to verify accuracy. Next, the levels of the substances
measured are reviewed and a risk determination is made. Then, if not
already done, an ultrasound exam will confirm the woman's correct
gestational age and rule out twins. If all the factors in the formula are
accurate, and the test result shows the woman to be at risk for a neural tube
defect, then some providers will order a second AFP test to confirm the first
abnormal result. AFP testing which includes HCG and UE3 measurements --
for example, the triple screen -- is done only once. Further testing is very
often recommended. If the woman is shown to be at increased risk for having
a baby with Down Syndrome, then amniocentesis is most often offered.
If the woman's fetus is shown to be at risk for having a neural tube defect or
an abdominal wall defect, then a special ultrasound examination called
LEVEL 2 or "TARGETED" might be advised. This exam is performed by a
physician with special training in ultrasonography. If the targeted ultrasound
exam does not show an abnormality, then amniocentesis may be
recommended. Sometimes additional targeted ultrasound examinations are
recommended when all further testing shows no abnormalities. Some fetuses
are at risk for growth abnormalities later in pregnancy.
Q. WHY IS AMNIOCENTESIS OFTEN RECOMMENDED WHEN
AFP TEST RESULTS ARE ABNORMAL?
Amniocentesis is the procedure used to withdraw a small amount of amniotic
fluid (the water in the sac surrounding the fetus). Amniotic fluid contains cells
shed from the fetus and includes copies of the genetic material the fetus
possesses. Tests done on amniotic fluid yield more accurate results than tests
on maternal blood. If the woman is determined to be at risk for having a
baby with a neural tube defect, then, along with the level 2 (targeted)
ultrasound exam, very often amniocentesis is recommended also.
Approximately 98% of all open neural tube defects can be detected by
testing amniotic fluid. If the fetus is at risk for having Down Syndrome, then
amniocentesis will detect this with greater than 99% accuracy when this
chromosome abnormality is present.
Q. HOW DO I OBTAIN AFP TESTING?
AFP testing can be done between 14 and 22 weeks along -- counted from
the first day of the last menstrual period -- but is best done at between 16
and 18 weeks. If amniocentesis is planned for other reasons, then serum
(blood) AFP testing will not be done. The amniotic fluid will be tested for
neural tube defects and Down Syndrome. If the woman has chorionic villi
sampling (CVS) early in pregnancy, which tests only the fetus' chromosomes,
she can have AFP testing at 16 weeks to screen for neural tube defects. Only
AFP will be measured since HCG and UE3 levels are only used to help
detect chromosome abnormalities, and CVs has already tested for this. If the
woman decides to have serum AFP testing, a special test request form will
be filled out with information about the woman and her pregnancy. This
information must be accurate to help avoid false abnormal results.
Q. WHEN MIGHT AFP TESTING BE RECOMMENDED?
All pregnant women should be informed of the availability of this prenatal
screening test for certain birth defects. Most providers suggest and explain
AFP testing, but it is not a mandatory test. Serum AFP testing is
recommended for all pregnant women up to the age of 35. lt can be done
after age 35, but usually amniocentesis or chorionic villi sampling is offered
when the woman will be age 35 or older by the time the baby will be due.
Some women are at increased risk for having a fetus with a neural tube
defect. They are those who have already had a child so afflicted, those with a
family history of neural tube defects and women with insulin-dependent
diabetes. Women who are at increased risk for having a baby with Down
Syndrome are those with a child who has Down Syndrome or who has a
family history of Down Syndrome and those who are age 35 years or older.
Q. WHAT ARE THE ADVANTAGES FOR HAVING AFP
TESTING?
Most women want to obtain as much information about their unborn baby as
they can. Neural tube defects and Down Syndrome are major birth defects.
Serum AFP testing can help identify those women who are at risk for having
a baby with those problems. Prior to the advent of ultrasound and prenatal
testing such as AFP testing, many abnormalities went undetected until the
time of birth. The sophistication of prenatal diagnostic testing is dynamic and
still evolving. Presently, every pregnant woman must ask herself how much
information she wants about her unborn baby. Choosing to have this test will
add to that knowledge.
Q. WHAT ARE THE DISADVANTAGES FOR CHOOSING TO
HAVE AFP TESTING?
The greatest disadvantage is the FALSE abnormal test result. Almost 50% of
abnormal test results occur because of incorrect information supplied for the
formula to calculate the result. This is why it is so important for the test
request form to be filled out accurately. Approximately 40 of every 1,000
women having serum AFP testing will have a result suggesting their fetus is at
risk for a neural tube defect. Of these 40 women, only one will actually have
a baby with a neural tube defect. Approximately 70 of every 1,000 women
having serum testing will have a result suggesting their fetus at risk for having
Down Syndrome. Of these 70 women, only one or two will actually have a
baby with Down Syndrome.
In summary, approximately 110 women of every 1,000 (11 of every 100, or
an 11% chance) having serum testing will have an abnormal result. For those
women with abnormal test results, further testing -- an ultrasound to confirm
the correct gestational age on the date the blood was drawn for the test
and/or amniocentesis -- will almost always confirm or rule out these
abnormalities. Parental anxiety over false abnormal test results is
probably our biggest concern. Serum AFP testing is an excellent prenatal
screening test, but like many things, it is not perfect.
Q. IS A PERFECT BABY GUARANTEED IF AFP TEST RESULTS
ARE NORMAL?
No. There is no test available that can provide an absolute guarantee. Serum
AFP testing is a screening test and will detect approximately 85% of fetuses
with open neural tube defects. The "triple screen" will detect 60% of fetuses
with Down Syndrome in women under age 35. There are many other types
of problems fetuses can have that AFP testing cannot detect. Also, there is a
one in 1,000 chance that the fetus will have a neural tube defect or Down
Syndrome and the AFP serum screening test result will be normal.
Q. SUMMARY
AFP testing is an excellent screening test designed to identify those pregnant
women who are most at risk for having a baby with certain birth defects.
Most women who have an abnormal screening test result will have a
normal baby. Discuss the implications of having this testing with your family
and healthcare provider. It is the pregnant woman's decision to proceed with
this testing. Read this information carefully. If you have any questions or need
clarification, please ask for it..