Amniocentesis
What is Amniocentesis?
Amniotic fluid is the fluid seen around the baby within the uterus. Amniocentesis is a procedure wherein a small amount of amniotic fluid is aspirated from the amniotic cavity without touching the baby for further testing. The fluid contains fetal cells and various other proteins which can help to determine the chromosomal and genetic abnormalities and provide valuable information about the baby’s health. It can also detect fetal infections. This procedure is also used to drain out the excess amniotic fluid. This is usually done from 16 weeks onwards.
The Procedure
A prenatal procedure in which around 20 ml of amniotic fluid containing fetal tissue is aspirated from the gravid uterus under ultrasound guidance, without disturbing the fetus. The fetal tissue is then examined for genetic disorders or chromosomal abnormality.
Indication
Genetic Tests
- Karyotyping is the commonest test done with the aspirated amniotic fluid or chorionic villous. It studies the number, size and shape of the chromosomes. It can pick up aneuploidies (missing/extra chromosomes). This helps to diagnose conditions like Down’s Syndrome, Turners Syndrome, Fragile X Syndrome, Deletions and Duplications.
- Micro Array can identify submicroscopic deletions and duplications which are not picked up by Karyotyping. It helps to diagnose conditions like Di George Syndrome, COPY number variant involved in IUGR, intellectual disability etc.
- Targeted Gene Panels are available for specific gene disorders like Spinal Muscular Atrophy, Deaf-mutism, Haemoglobinopathies etc.
- Prenatal Clinical/Whole Exome Sequencing is rarely used. It is helpful for detailed analysis of genetic material in conditions such as suspected skeletal disorders which can be due to variable mutations and not due to a single gene mutation.
"High-risk" for Down's syndrome on screening tests (combined, triple or quadruple marker)