PRENATAL DIAGNOSIS:

Parents are always concerned about the health of their unborn baby.  Most women give birth to healthy babies, but certain mothers have an increased risk of giving birth to a baby with a birth or genetic defect.  Personal and family medical histories provide imporant information together with physical exams, various procedures (sonargraphy, sonor immages) and biochemistry to help identify women who may be at risk to have a baby a genetic or birth defect.  Pregnant woman women with an increased risk benefit from prenatal diagnostic procedures.

There are three different prenatal diagnosic procedues that may be offered to parents where the pregnancy is at risk namely Amniocentesis (Amnio), Chorionic Villus Sampling (CVS) and chordocentesis (chord blood sampling). The  procedure followed is determined by the pregnancy duration and the choice of the consulting doctor (gynaecologist and / or sonagrapher).

WHO SHOULD CONSIDER PRENATAL DIAGNOSTIC PROCEDURES?

Couples, together with their doctor can decide whether there will be a benefit from the information provided by the results of the prenatal diagnostic procedure.  Each woman’s case is different. Prenatal diagnostic procedures may be recommended for:

  • Women who will be 35 or older at delivery have an increased risk for a baby with a chromosome abnormality.
  • Couples who have had a baby with a known genetic, chromosome or  birth defect
  • Couples who have a relative with a chromosome abnormality (e.g. Down syndrome), mental retardation, a medical history of a genetic disorder, or other birth defects.
  • Couples who have experienced two or more pregnancy losses (spontaneous abortions, stillbirths, or neonatal deaths).
  • Couples with an increased risk of having a baby affected with Down syndrome based on  first or second trimester prenatal screening.
  • Couples who are concerned about having an abnormal baby. (especially maternal anxiety)

PRENATAL DIAGNOSTIC PROCEDURES:

Amniocentesis
Amniocentesis is a medical procedure in which a small amount of amniotic fluid is withdrawn from the amniotic sac surrounding the fetus in the uterus. An amniocentesis is ideally performed between 14 and 22 weeks gestation.

  

WHICH TESTS CAN BE PERFORMED ON AMNIOTIC FLUID SAMPLES:

Several different tests may be performed using the amniotic fluid specimen. Specific tests are performed depending on the indications. 

Chromosome analysis:

The cells from the foetus flouting in the amniotic fluid are cultured in a culture medium containing nutrients to sustain growth. Metaphase plates from cultured foetal cells are used for chromosome analysis. More than 99.9% of foetal chromosome abnormalities can be detected by the analysis of G-banded metaphase chromosomes. The prenatal chromosome analyses performed by highly experienced qualified staff in our laboratory are very accurate and reliable.

Open Neural Tube Defects (Open spine and open skull defects):

Approximately 99% of all open neural tube defects may be detected by a detailed ultrasound examination and by determining the foetal alpha-fetoprotein (AFP) level in the amniotic fluid. Neural tube defects which are too small or covered by skin cannot be detected by these tests. Ultrasound alone does not detect all of the anomalies.

Inherited genetic disorders

Couples that are known carriers of genetic disorders with defined mutations may be offered prenatal diagnosis for that disorder. Carrier testing Cystic Fibrosis, Sickle Cell, Fragile (X), Huntington. 

Normal results from these tests do not eliminate the possibility your baby may have birth defects and/or mental retardation not detectable by these tests.

 

CHORIONIC VILLUS SAMPLING (CVS)


CVS is a medical procedure where a  performed between 10 - 13 weeks gestation in (a tissue on the outside of the fetal gestational sac) is obtained for culture and chromosome analysis.

 

 

WHICH TESTS CAN BE PERFORMED BY CVS?


Specific tests are performed depending on the indications.

Chromosome analysis

In the laboratory, the Cells obtained from the CVS procedure are cultured in the laboratory using special nutrient medium to sustain growth. Chromosomes obtained from the cultured CV cells are then analyzed.  The prenatal test accurately detect about 99% of chromosome abnormalities.

Inherited genetic disorders

Known carriers of genetic disorders which have defined mutation that can be detected DNA analysis CV cells, may be offered a prenatal test.  Examples of  disorders for which carrier prenatal diagnosis may be offered include Cystic Fibrosis,  Sickle Cell and Fragile (X). Normal test results do not eliminate the possibility the baby may have birth defects and/or mental retardation tested for by these tests.  

Open neural tube defects which cannot detected by CVS procedures and  a maternal serum alpha-fetoprotein (MSAFP) blood test and/or an ultrasound examination performed at 14 - 16 weeks gestation is advised. These tests detect most, but not all pregnancies with open neural tube defects.

CORDOCENTESIS

Cordocentesis is a medical procedure performed after 22 weeks gestation, mostly in cases where patients visit the doctor to late for any other prenatal procedure.  A fetal blood sample is obtained from the umbelical cord.  This fetal blood sample is used for culture and fetal chromosomal analysis.

 

WHICH TESTS CAN BE PERFORMED ON CORD BLOOD:

Several different tests may be performed using the blood sample obtained by cordocentesis. Specific tests are performed depending on the indications. 

Chromosome analysis:

The leukocytes from the foetus cultured in a culture medium containing nutrients to sustain growth. Metaphase plates from cultured foetal cells are used for chromosome analysis. More than 99.9% of foetal chromosome abnormalities can be detected by the analysis of G-banded metaphase chromosomes. The prenatal chromosome analyses performed by highly experienced qualified staff in our laboratory are very accurate and reliable.

Inherited genetic disorders

Couples that are known carriers of genetic disorders with defined mutations may be offered prenatal diagnosis for that disorder. Foetal DNA is extracted from the foetal blood obtained by cordocentesis. The DNA can be tested known disease causing mutations for disorders like Cystic Fibrosis, Sickle Cell, Fragile (X), Huntington’s disease and many more. 

Normal results from these tests only eliminate the specific disease causing mutation/s tested for.  The possibility that baby may have a birth defects and/or mental retardation not detectable by these tests cannot be eliminated.

WHAT IS A CHROMOSOME ABNORMALITY?

Chromosomes are units of genetic information.  Babies with a chromosome abnormality usually have mild to severe mental retardation and birth defects.  The most common chromosome abnormality is Down syndrome.  A chromosome test is performed on cells from the placental tissue (chorionic villi) to determine if the fetus has a chromosome abnormality.  The test can also reveal the chromosomal sex of the fetus. 

Chromosome abnormalities are caused at conception when an abnormal sperm or egg from one parent fuses with a normal sperm or egg from the other parent.  The abnormal sperm or egg contains extra or missing chromosome material.  These abnormal sperm or eggs appear to be present in everyone, but the risk of an abnormal conception increases significantly with the parents' ages.