DIAGNOSTIC TESTS FOR DOWN SYNDRONE (DS)

…include 3 different invasive techniques:

1. Amniocentesis
2. Chorionic Villus Sampling (CVS)
3. Percutaneous Umbilical Blood Sampling (PUBS) or Fetal Blood Sampling

1. AMNIOCENTESIS

1. BRIEF OUTLINE

This procedure involves the collecting of a small sample of amniotic fluid (about 15mLs) via a thin needle through the abdominal wall and into the uterus (under the guidance of an ultrasound scan) Usually carried out at weeks 14-18 of gestation.

2. AMNIOTIC FLUID

The amniotic fluid is found in the amniotic sac. The amniotic sac is a tough pair of membranes that holds the embryo. It holds fluids which allow the embryo to move and cushions it during development. It is in this fluid that fetal cells that the fetus sheds can also be found.

- The inner membrane (the amnion) contains the amniotic fluid & fetus

- The outer membrane (the chorion) contains the amnion and is part of the placenta

3. PROCEDURE

- Antiseptic fluid is used to clean the area of the abdomen.

- A very thin needle enters through the abdominal wall and into the uterus

- A sample is collected via syringe and the cells sent to a laboratory

- Cells are allowed to grow and multiply until there is enough to tests

4. RESULTS

Results from a full karyotyping usually takes 2-3 weeks, however, a rapid test (2 days) may be carried out on the chromosomes most commonly associated with disorders (21, 13, 18, X & Y)

A positive result should initiate the doctor to provide information to the parents about Down syndrome and counseling may be offered to aid parents make an informed decision as to keep or terminate the fetus.

However, a negative result does not mean the baby has a 0% chance of developing chromosomal abnormalities at birth.

5. RISKS

The risk of this procedure is less than 1% and if miscarriages were to be a result of this procedure, it would occur usually within a few weeks of this test.

Some of the common risks are:

- bleeding from puncture

- infection

- premature rupture of the amniotic sac

- injury to the baby

6. RECOMMENDATIONS/WHO SHOULD TAKE THE TEST

- Women over the age of 40 years (Victorian women aged 37 years and over are routinely offered this test).

- Women with a family history of chromosomal abnormalities, such as Down's syndrome.

- Women who have already had children with chromosomal abnormalities.

- Women known to be carriers of genetic diseases.

- Women with partners who have a family history of a genetic disorder or chromosomal abnormality.

- Women who return an abnormal 'serum screen' blood test or ultrasound examination result.

2. CHORIONIC VILLUS SAMPLING

1. BRIEF OUTLINE

Involves removing tiny pieces of tissue from the placenta either via a needle through the abdomen or via a catheter inserted through the vagina and into the cervix. It carried out earlier than Amniocentesis at 10-12^th week of pregnancy.

2. CHORIONIC VILLI

These are tiny finger-like growth found in the placenta and contain the same DNA as the baby’s cell.

3. PROCEDURE RISKS AND RECOMMENDATIONS

Procedure is similar to Amniocentesis; however the risks are a little higher (although still roughly about 1% of miscarriages). Results are obtained similarly through karyotypes or rapid sampling. Recommendations for taking this test are similar to the Amniocentesis Test.

3. PERCUTANEOUS UMBILICAL BLOOD SAMPLING

1. BRIEF OUTLINE

This test is usually carried out after 18 weeks and is done when CVS and Amniocentesis Tests fail to give clear results. It involves taking a blood sample from the umbilical cord of the baby for further testing similar the other tests. Risks and procedures are similar as is recommendations.

Also found something called preimplantation diagnosis for IVF babies. Couldn’t find much information on it though. Sorry!

RESOURCES:

http://www.pregnancy-info.net/fetal_blood_sampling.html

http://www.webmd.com/baby/Chorionic-Villus-Sampling-CVS

http://www.wcox.com.au/cvs.htm

http://www.kidshealth.org/parent/medical/genetic/down_syndrome.html

http://www.ucsfhealth.org/childrens/medical_services/preg/prenatal/conditions/down/diagnosis.html

http://www.wcox.com.au/amniocen.htm

http://www.betterhealth.vic.gov.au/bhcv2/bhcarticles.nsf/pages/Amniocentesis?open