A sample of the amniotic fluid is taken to do a prenatal test that allows the doctor to find out about the health of the baby. Amniotic fluid is the liquid that is present in the uterus and surrounds the baby.
Amniocentesis is the prenatal test and is done to check whether the baby has any genetic disorder or any chromosomal abnormality such as a down syndrome.
Chorionic villus sampling or CVS, which is also a method to check for chromosomal abnormalities in babies, is where the doctor uses chorionic villi which are small projections on the placenta and are fingerlike and is used to take cells. The cells are then sent to the lab to do a genetic analysis on them.
Both the procedures are done in the first trimester where a karyotype is produced, that is the picture of the baby’s chromosomes, and the doctor will check for any problems.
The test is carried out when the woman is between the 16th and the 20th week of pregnancy. Most women do not go for this test and only those who have a high risk of having babies that may have any chromosomal or genetic problems opt for this test. This is because the test is very invasive and also carries a small chance of miscarriage.
Reason for doing Amniocentesis
The following reasons are why one may be required to do an Amniocentesis test:
To rule out the intrauterine infection
To check the baby in case the mother has Rh sensitization. This is a complex condition that occurs when the mother’s blood is of a different type than the babies.
To check the lungs of the baby in case the mother has been advised an early delivery because of any medical condition.
Disorders that can be detected by doing the test
The Amniocentesis test helps to detect the following conditions:
Chromosomal disorders which include Down syndrome, trisomy 13 and 18, and any abnormalities with the sex chromosomes. The test cannot, however,f measure how severe the condition is
Genetic disorders like sickle cell disease, cystic fibrosis, and Tay-Sachs disease. The test helps to find out if the baby has any of these diseases
The test measures the alpha-fetoprotein (AFP) in the amniotic fluid which is used to find out if the baby has any neural tube defect like anencephaly or spina bifida.
The Amniocentesis test cannot detect any birth defects that are structural like cleft lip or a heart malformation. Thus many of these structural defects can only be found about in the second trimester when an ultrasound is done.
Miscarriage risk from Amniocentesis
The risk of having a miscarriage on doing an Amniocentesis is very low. Most of the women who have babies with a genetic or a chromosomal defect will end up having a miscarriage in the second trimester and thus one cannot be sure whether the miscarriage was actually caused because of the test procedure. However, as per the estimates, the loss rate is lower than 1 in 300 when done by a doctor who has a lot of experience in doing amnios.