Prenatal diagnosis uses both invasive and non-invasive techniques to find out the health of a fetus. Prenatal diagnosis helps in making decisions whether to terminate the pregnancy or to continue with it.
A variety of both invasive and non-invasive techniques are used for prenatal diagnosis. Each technique can be used at a specific time of the pregnancy. Some of the techniques such as ultrasonography, amniocentesis, chronic villus sampling, fetal blood cells in maternal blood, maternal serum alpha-fetoprotein are used in prenatal diagnosis.
Ultrasonography is a harmless technique to both the fetus and the mother; it can be used to determine any form of abnormalities in fetal anatomy during 16 to 20 weeks gestation. This technique can be used to determine the size of the fetus and placenta and also the amount of amniotic fluid. Ultrasonography cannot be used to determine some abnormalities like Down syndrome.
Amnoicentesis and Chorionic Villus Sampling
Amnoicentesis and chronic villus sampling both are invasive procedurs used in prenatal diagnosis. Both techniques require fetal cells extracted directly from the uterus. Fetal cells extracted from these methods are cultured in laboratory and can be used for chromosomal analysis, biochemical analysis and also molecular analysis. The major risk of invasive technique is that, they carry a small around 1% risk of miscarriage.
Maternal Blood Sampling for Fetal Blood Cell:
This technique uses the known phenomenon such as fetal blood cells through the placental villi gain access to maternal blood circulation system. Fetal cells are identified using fluorescence in-situ hybridization (FISH) technique. FISH can be used to diagnose the chromosomal abnormalities such as trisomies and monosomy X.
Maternal serum alpha-fetoprotein (MSAFP)
Maternal serum alpha-fetoprotein can be used to determine the level of fetal alpha-fetoprotein, since adults usually have albumin in the blood. Maternal serum alpha-fetoprotein can be used to determine the neural tube defects in the unborn fetus. Technique can also be used to determine the trisome syndromes such as Down syndrome and also other chromosomal abnormalities if present.
Cell-Free Fetal Nucleic Acid (cffNA)
Fetal DNA fragments can be found in the mother's blood circulation system after 7 weeks of pregnancy. Non-invasive prenatal diagnosis technique uses this cell-free fetal nucleic acid fragments to analyze chromosomal abnormalities.
Major challenge of this technique is identifying fetal DNA in mother's circulation system because only small quantity of fetal DNA is present in the mother's blood, and also the 50% of genetic code are same or identical between mothers and foetus.
To overcome these limitations researchers are identifying fetal specific DNA markers. For example genes such as mapsin and RASSFIA are silent in adults, so these are used as markers in identifying cell-free fetal nucleic acid.
This new non-invasive technique can be used to determine sex, single gene disorder, aneuploidy and also rhesus blood group incompatibility.
Advantages of Prenatal Diagnosis:
1. Prenatal diagnosis helps in managing the pregnancy.
2. Prenatal diagnosis helps in determining the pregnancy outcome.
3. Prenatal diagnosis helps in identifying possible complications may occur during the time of child birth .
4. Prenatal diagnosis helps in identifying possible complications may occur in the newborn.
5. Prenatal diagnosis also helps in deciding whether to continue with the pregnancy or not.
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