Prenatal diagnosis is a test performed during pregnancy to determine the health of the unborn fetus. Congenital anomalies account for 20 to 25% of perinatal deaths. Prenatal diagnosis is carried out to perform genetic testing of the fetus to conclude if the developing baby has a genetic problem.
There are a variety of non-invasive and invasive techniques available for prenatal diagnosis. Each of them can be applied only during specific periods of gestational age .
The non-invasive techniques includes:
Non invasive prenatal testing (NIPT):
Non invasive prenatal diagnosis (NIPT) is a simple blood test without any risk to the mother or the baby, in which a blood sample is collected from the mother. This technique makes use of the phenomenon of fetal blood cells gaining access to maternal circulation through the placental villi. Only a very small number of fetal cells or cell free DNA enter the maternal circulation in this fashion that can be tested for the most common fetal chromosomal aneuploidies including chromosomes 13,18,21,X and Y. NIPD is done starting from 10 weeks of gestational age.
The invasive techniques includes:
Amniocentesis:
This is an invasive procedure in which a sample of the amniotic fluid is collected by special needle that is passed through the mother's lower abdomen into the amniotic cavity inside the uterus. Amniocentesis is performed between 14 and 20 weeks gestation. However, an ultrasound examination always proceeds amniocentesis in order to determine gestational age, and provides a better visualization of the fetus and placenta. Within the amniotic fluid are fetal cells which can be tested for chromosome analysis, biochemical analysis, and molecular genetic analysis.
Risks with amniocentesis are uncommon, it includes fetal loss and maternal Rh sensitization. The increased risk for fetal mortality following amniocentesis is about 0.5% above what would normally be expected.
Chorionic Villus Sampling (CVS)
In this procedure, a sample from the placental chorionic villi is collected by a catheter or specialised syringe that is passed either through the vagina or transabdominally under ultrasound guidance. These cells can be tested for chromosome analysis, biochemical analysis, and molecular genetic analysis. CVS can be safely performed between 9.5 and 12.5 weeks gestation. The risk of CVS include morbidity for the fetus at a rate of 0.5 to 1% higher than for women undergoing amniocentesis. The possibility of maternal Rh sensitization is present. There is also the possibility that maternal blood cells contamination when the sample is collected.
