Importance of Prenatal Diagnosis
Prenatal testing, screening, and diagnosis are very important tools to assess the genetic disorders of congenital anomalies of an unborn fetus.
There are five (5) types of prenatal genetic tests that can be used for screening the risk of the genetic disorder in a baby or for diagnosing such abnormalities.
- Maternal blood serum
- Prenatal ultrasounds
- Non-invasive prenatal testing
- Chorionic villus sampling
- Evaluating the risk of genetic problems
- Offered to all pregnant women
- Confirm or rule out genetic problems
- offered after abnormal screening tests or known risk factors
Screening for Aneuploidies
Advanced testing called aneuploidy screening helps to identify missing abnormal chromosomes that could cause miscarriage or life-altering disorders.
First-trimester screening is a prenatal test that offers early information about a baby's risk of certain chromosomal conditions, specifically Down syndrome (trisomy 21) and extra sequences of chromosome 18 (trisomy 18).
It is taken usually between 10 weeks and 13 weeks of pregnancy when CRL is 31 to 52 mm.
It includes a test of the pregnant women's blood and an ultrasound exam. The ultrasound exam called a Nuchal Translucency Screening measures the thickness of space at the back of the fetus's neck. An abnormal measurement shows that there is an increased risk of Down syndrome or another type of aneuploidy. It is also linked to physical defects of the heart, abdominal wall, and skeleton.
It includes the following test called the Quad or Quadruple blood test that measures the levels of four different substances in the blood. The quad test screens for Down syndrome, Edwards syndrome, NTD's (Neural tube defects), and abdominal wall defects.
Ideally, it is done between weeks 15 and 18.
However, the procedure can be done up to week 22.
This is a noninvasive procedure for both the fetus and the mother. It can be quite useful to determine the size and position of the placenta, the fetus, the amount of amniotic fluid, and the appearance of fetal anatomy.
For prenatal diagnosis, amniocentesis is performed between 14 to 20 weeks gestation. It is an invasive procedure. It is diagnostic genetic testing offered to pregnant women with a higher risk of having a child with genetic abnormalities and those with positive screening tests.
Amniocentesis test helps to diagnose genetic disorders and neural tube defects like Down syndrome, sickle cell anemia, spina bifida, and cystic fibrosis.
A small sample of amniotic fluid from the uterus is withdrawn with a long thin needle guided by ultrasound.
Chorionic Villus Sampling
It is prenatal genetic testing that can be offered to women between the tenth and the 13th weeks of pregnancy to confirm or rule out that their child has certain genetic conditions.
A thin tube is guided through the cervix or a needle is inserted into the uterus to remove a sample of Chorionic villus cells from the placenta.
There will be slight discomfort. An injection of local anesthesia will be given before the procedure.
It helps to diagnose chromosomal abnormalities such as down syndrome and Edwards syndrome, then genetic conditions such as cystic fibrosis and sickle cell anemia.
Preliminary results are ready in 2 to 3 days. The complete analysis will be ready in 10 days.
It is also known as percutaneous umbilical blood sampling. It is a diagnostic prenatal test. In this procedure, a needle is inserted directly into the fetal umbilical vessel under ultrasound guidance and removes 1 to 4 ml of fetal blood.
It helps to detect chromosome abnormalities and certain blood disorders with high levels of accuracy. It may be performed to help diagnose any of the following concerns:
- Malformations of the fetus
- Fetal infection - toxoplasmosis, viral.
- Fetal platelet count in the mother
- Fetal anemia, bleeding disorders, hemoglobinopathies.
- Iso immunization However it does not allow testing for neural tube defects.
Local anesthesia is given before the procedure, So there will not be any pain except a little discomfort. Between weeks 18 to 23 of pregnancy, Cordocentesis test will be taken.
Pregnant women older than 35 years, couples related genetically, couples already with a child affected with a genetic disorder, women who used alcohol or drugs before or during pregnancy.
It is a Non-Invasive Prenatal Test. Pregnant women older than 35 years, couples related genetically, couples already with a child affected with a genetic disorder, women who used alcohol or drugs before or during pregnancy.
NIPT is 99.9 percentage accurate and it is performed around 10th week of pregnancy through a blood test.