Here are a selection of optional tests used to screen for a variety of possible
abnormalities.
Amniocentesis?
It is procedure in which an obstetrician withdraws a small amount of the amniotic
fluid (about 20 cc) surrounding the fetus.
This is done by inserting a thin hollow needle through the mother's abdomen into
the uterus. The obstetrician will use ultrasound to guide the needle during the procedure so as not to harm the unborn child.
The procedure is performed on an outpatient basis and takes only a few minutes.
The needle will cause some pain when it penetrates the uterus, but the pain should
not last long and should not hurt more than an injection into any other part of
the body.
After the fluid has been withdrawn, the removal of the needle should cause no further
discomfort. The fluid is then sent to the laboratory for special tests.
Why Is Amniocentesis Necessary?
The majority of amniocentesis is done for the detection of chromosomal disorders.
Chromosomes carry genes that pass certain characteristics from parents to their
children. When there are too many or too few chromosomes, or there is defect in
a chromosome, birth defects usually occur.
Down Syndrome is the most common chromosomal disorder. It causes mental retardation
and other health problems such as heart defects. Other less common chromosomal disorders
may lead to serious handicaps and death.
When Is Amniocentesis Done?
Amniocentesis is usually done between 16th week but before the 20th week of pregnancy.
When Will The Amniocentesis Test Results Be Available?
Usually it takes about 3 - 4 weeks to complete the laboratory tests.
Can All Birth Defects Be Detected By Amniocentesis?
No. Amniocentesis can detect almost all known chromosomal disorders. However, birth
defects not due to chromosomal abnormalities cannot be detected through this test.
Who Should Consider Amniocentesis?
Women who are 35 years of age or older at delivery. This is because their children
are at an increased risk of chromosomal disorders such as Down Syndrome.
Women who have had a child with Down Syndrome or other chromosomal disorders.
Women who know that they or the baby's father have an unusual chromosome arrangement.
There may be other reasons that apply uniquely to you. Both you and your obstetrician
should decide together if you need an amniocentesis.
Is Amniocentesis Safe?
Amniocentesis is a safe, low risk procedure when done by experienced medical experts.
The risk of miscarriage following the test is reported to be 0.3 - 0.5%.
Useful Information
Activity: You should be able to return to your normal activities within a few hours
after the procedure. You may have your bath as usual. Diet: There are no dietary
restrictions relating to this procedure. Medication: No medication is required following
this procedure.
Return To The Hospital Or Call Your Obstetrician If :
- You run a fever
- You feel nauseated and vomit
- You experience pain in the shoulder
- You experience any unusual lower abdominal pain
- You notice vaginal bleeding
- You notice leakage of fluid from the vagina
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Chorionic Villus Sampling
It is a procedure in which an obstetrician withdraws a small amount of the placenta
tissue.
This is done by inserting a biopsy needle through the mother's abdomen into the
placenta. The obstetrician will use ultrasound to guide the needle during the procedure
so as not to harm the unborn child. For this procedure, local anaesthesia will be
given.
The procedure is performed on an outpatient basis and takes only a few minutes.
The needle will cause some pain when it penetrates the uterus, but the pain should
not last long and should not hurt more than an injection into any other part of
the body.
After the tissue has been withdrawn, the removal of the needle should cause no further
discomfort. The tissue is then sent to the laboratory for special tests.
Why Is Chorionic Villus Sampling Necessary?
Chorionic villus sampling is done for the detection of chromosomal disorders
and genetic diseases such as thalassaemia.
Chromosomes carry genes that pass certain characteristics from parents to their
children. When there are too many or too few chromosomes, or there is a defect in
a chromosome, birth defects usually occur.
Down Syndrome is the most common chromosomal disorder. It causes mental retardation
and other health problems such as heart defects. Other less common chromosomal disorders
may lead to serious handicaps and death.
Thalassemia is an inherited blood disease, which is transmitted by a gene. If both
parents have the thalassamia trait, the chance of having a child with thalassaemia
major is 25%.
When Is Chorionic Villus Sampling Done?
Chorionic villus sampling is usually done between 10th to 12th week of
pregnancy.
When Will The Chorionic Villus Sampling Test Results Be Available?
Usually it takes about 3 - 4 weeks to complete the laboratory tests.
Can All Birth Defects Be Detected By Chorionic Villus Sampling?
No. Chorionic villus sampling can detect almost all known chromosomal disorders.
It can also check for specific genetic disease.
Who Should Consider Chorionic Villus Sampling?
- Women who are 35 years of age or older at delivery. This because their children
are at an increased risk of chromosomal disorders such as Down Syndrome.
- Women who have had a child with Down Syndrome or other chromosomal disorders.
- Women who know that they or the baby's father have an unusual chromosome arrangement.
- If both parents are thalassaemia carriers.
- There may be other reasons that apply uniquely to you. Both you and your obstetrician
should decide together if you need a chorionic villus sampling.
Is Chorionic Villus Sampling Safe?
Chorionic villus sampling is a safe, low risk procedure when done by experienced
medical experts. The risk of miscarriage following the test is reported to be 1%.
Useful Information
Activity: You should be able to return to your normal activities within
a few hours after the procedure. You may have your bath as usual. Diet: There are
no dietary restrictions relating to this procedure. Medication: No medication is
required following this procedure.
Return To The Hospital Or Call Your Obstetrician If :
- You run a fever
- You feel nauseated and vomit
- You experience pain in the shoulder
- You experience any unusual lower abdominal pain
- You notice vaginal bleeding
- You notice leakage of fluid from the vagina
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Fetal Blood Sampling
It is a procedure in which an obstetrician withdraws blood from the umbilical cord
of the fetus.
This is done by inserting a thin hollow needle through the mother's abdomen into
the umbilical cord. The obstetrician will use ultrasound to guide the needle during
the procedure so as not to harm the unborn child.
The procedure is performed on an outpatient basis and takes only a few minutes.
The needle will cause some pain when it penetrates the uterus, but the pain should
not last long and should not hurt more than an injection into any other part of
the body.
After the fetal blood has been withdrawn, the removal of the needle should cause
no further discomfort. The fluid is then sent to the laboratory for special tests.
Why Is Fetal Blood Sampling Necessary?
The majority of fetal blood sampling is done for the detection of chromosomal
disorders, genetic diseases and viral infection.
Chromosomes carry genes that pass certain characteristics from parents to their
children. When there are too many or two few chromosomes, or there is a defect in
a chromosome, birth defects usually occur.
Down Syndrome is the most common chromosomal disorder. It causes mental retardation
and other health problems such as heart defects. Other less common chromosomal disorders
may lead to serious handicaps and death.
When Is Fetal Blood Sampling Done?
Fetal Blood Sampling is usually done between 20th and 23rd week of pregnancy.
When Will The Fetal Blood Sampling Test Results Be Available?
Usually it takes about 1 - 2 weeks to complete the laboratory test.
Can All Birth Defects Be Detected By Fetal Blood Sampling?
No. Fetal blood sampling can detect almost all known chromosomal disorders. It can
also check for specific genetic disease and viral infections.
Who Should Consider Fetal Blood Sampling?
- Any patient with fetal abnormalities detected during ultrasound screening.
- Any patient who is more than 20 weeks pregnant and is at high risk of having a
chromosomal disorder.
- If both parents are thalassaemia carriers.
- There may be other reasons that apply uniquely to you. Both you and your obstetrician
should decide together if you need a fetal blood sampling.
Is Fetal Blood Sampling Safe?
Fetal blood sampling is a safe, low risk procedure when done by experienced medical
experts. The risk of miscarriage following the test is reported to be 2 - 5%.
Useful Information
You should be able to return to your normal activities within
a few hours after the procedure.
You may have your bath as usual.
Diet: There are no dietary restrictions relating to this procedure.
Medication: No medication is required following this procedure.
Return To The Hospital Or Call Your Obstetrician If :
- You run a fever
- You feel nauseated and vomit
- You experience pain in the shoulder
- You experience any unusual lower abdominal pain
- You notice vaginal bleeding
- You notice leakage of fluid from the vagina
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Maternal Serum Screening
Maternal Serum Screening Test is a voluntary blood test conducted between 15 and
20 weeks of pregnancy to aid in the risk assessment of Down Syndrome, a congenital
disease caused by a defect in the chromosomes.
What Is The Test For?
The Maternal Serum Screening test is used to identify pregnancies in which the risk
of Down Syndrome is significant enough to justify considering an amniocentesis.
How Does It Work?
Conducted between 15 to 20 weeks of pregnancy, the test measures the amount of AFP
(alpha-fetoprotein) and hCG (human chorionic gonadotrophin). These substances are
produced by the foetus and the placenta, and can be detected in the mother's blood.
Together with mother's age, the measurements of AFP and hCG are used to calculate
her risk of carrying a baby with Down Syndrome. The test provides the mother with
her individual risk of having a baby with Down Syndrome. This numerical risk is
classified into either "low-risk" or "high-risk" using a cut-off risk of 1 in 250
to help mothers decide whether or not to go for an amniocentesis.
Why Measure These Substances?
We know that women with low AFP in their blood may have a higher than average risk
of having a baby with Down Syndrome. It appears that babies with Dow Syndrome tend
to produce less AFP than normal babies, and therefore less of it is transferred
to the mother.
The level of hCG tends to be higher when Down Syndrome is present.
The reason of these differences is not known. However, a delay in maturity of Down
Syndrome babies may be a cause as these two substances are associated with foetal
maturity.
The measurement of these substances helps doctors to estimate more accurately a
mother's risk of carrying a baby with Down Syndrome.
What Does The Test Result Mean?
In pregnancies with increased risk for Down Syndrome, the amount of AFP is lower
and the amount of hCG is higher.
A "high risk" result does not mean that the baby has Down Syndrome. It only means
that there is an increased risk that causes enough concern for your specialist to
offer an amniocentesis (a diagnostic test for Down Syndrome) to confirm or refute
the presence of a Down Syndrome pregnancy.
Likewise, a "low risk" result is not a guarantee that your baby will be healthy.
If your test shows a "low risk" result, it means there is a lower chance of a Down
Syndrome baby being born, so no further action is usually required.
Example
Your individual risk is quoted as 1 in 250. What this means is that out of 250 pregnancies,
only one of them will be affected and 249 will be normal.
If your risk is shown to be more than 1 in 250 of having a baby affected by Down
Syndrome (for example 1 in 50), you will be offered an amniocentesis to confirm
or refute the presence of Down Syndrome.
Why Is The Serum Test Done Between 15 And 20 Weeks of A Pregnancy?
Experience has shown that the blood test works best between 15 and 20 weeks
of pregnancy. Having the test conducted during this period allows time for intervention,
if needed, before the pregnancy is more advanced. It has also been shown that the
risk calculated is more accurate if an ultrasound scan has been done to confirm
the age of the pregnancy and to exclude multiple pregnancies.
Can The Test Screen For Other Types Of Abnormality?
Yes. The test can also indicate if there is an increased risk for other
abnormalities, particularly open spina bifida, a defect of the backbone. This is
indicated by the presence of a high AFP level. When this happens, a detailed ultrasound
scan will usually be arranged for further investigation.
What Happens When An Abnormality Is Discovered After Amniocentesis Or During
An Ultrasound Scan?
Your specialist will provide you with detailed information about the abnormality
discovered and how it may affect your baby. You may decide to terminate the pregnancy
if it is a major abnormality.
If The Test Result Is "Low Risk", Does it Guarantee That The Baby Will Be Healthy?
No. The screening test is not a guarantee that the baby will be healthy.
It only helps to screen for Down Syndrome and spina bifida. If the test result is
"low risk", it means that the chances of having these conditions are reduced.
Overall, about 6 -7 out of 10 Down Syndrome babies will be detected by the serum
screening. However, there will be still be some that are undetected and will be
born to mothers who have had a "low-risk" result.
Using a cut-off risk of 1 in 250, the rate of detection among mothers at "high risk"
has been shown to vary according to the maternal age as indicated below :
Maternal age Detection rate
- Less than 20 years 46 %
- Between 20 - 24 years 47 %
- Between 25 - 29 years 50 %
- Between 30 - 34 years 60 %
- Between 35 - 39 years 77 %
- Over 40 years 91 %
Do I Need The Test?
The test is entirely voluntary. In deciding whether or not to have the test, you
should consider carefully what you and your spouse would do if the test reveals
an increased risk of Down Syndrome or other abnormalities.
What Should I Do If I Would Like To Go For The Maternal Serum Screening Test?
Please inform your doctors if you wish to have the test. You will then be given
an appointment for the blood test between 15 to 20 weeks of your pregnancy based
on an ultrasound scan.
A Word Of Reassurance
The great majority of babies are healthy. Reading the information here may have
started you worrying about some possible problems with your pregnancy. Please keep
in mind that the great majority of babies are born perfectly healthy. For most women,
the test is likely to provide further reassurance that all is well.
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The information is provided by KK Hospital - Singapore’s leading Women and Children’s
Hospital. Please visit www.kkh.com.sg for more information.
